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					                                 Waste Water Treatment

putri nora novera mindra



Dear Rekan Milis,

Mohon informasinya tentang waste water, treatment2 yg diperlukan, kualitas air buangan (kira2
bisa dapat infromasi darimana ya?)
Dan apakah perbedaan treatment untuk wastewater di onshore & offshore, khususnya industri oil n
gas
Maaf kalau pertanyaannya terlalu banyak, saya masih awam ttg waste water ini
Terimakasih..


Thomas Yanuar

Mbak Putri,
Berikut sekilas rangkuman diskusi waste water dimilis kita ini dan silahkan dibandingkan dengan
WTP secara umum. Selengkapnya, bisa dibuka di Buku Pintar Migas Indonesia.
Karena lumayan panjang, ada baiknya di print supaya lebih mudah mencernanya.

Ini tulisan Pak Adhi Budhiarto: (silahkan Mbak Putri kontak beliau juga) Sebenernya ulasan
mengenai Sour Water Stripping unit sudah tercakup dalam tulisan saya untuk Buku Pintar Migas
Indonesia berjudul Teknologi Proses Kilang Minyak Bumi, yaitu di Bab XII Sour Water Stripping
Unit (mungkin tinggal tunggu waktu aja untuk di-release/di-upload ke server website sama mas
Budhi).

Karena tulisan tersebut belum sempet di-upload oleh mas Budhi, mungkin bisa saya sarikan
sebagai berikut :

Pengolahan limbah cair di petroleum industry (terutama di kilang) dilakukan melalui 2-3 tahap,
yaitu diolah di Sour Water Stripping unit dan di Oil Separator (dan biotreatment).

Biasanya untuk plant yang ada H2S nya dilengkapi dengan Sour Water Stripping (SWS) unit untuk
mengolah limbah cairnya sebelum kemudian dikirim ke Waste Water Treatment Plant (oil separator
& biotreatement). Untuk di petroleum industry, unit SWS biasanya terdiri dari :

1. Degassing Drum

Di degassing drum ini dilakukan pemisahan 3 macam komponen feed SWS, yaitu gas hydrocarbon
ringan dan H2S, minyak, dan air.
* Gas hydrocarbon ringan dan H2S yang terkandung dalam feed SWS masuk ke dalam degassing
drum dan menuju bagian degassing drum yang dilengkapi dengan packing column. Packing
column ini berisi 1" ceramic rashing ring packing. Di packing column ini, gas hydrocarbon ringan
dan H2S dikontakkan dengan stripped water produk SWS Column untuk mengambil kandungan
hydrocarbon berat yang mungkin terikut gas. Hydrocarbon berat yang di-absorb tersebut kemudian
masuk kembali ke dalam degassing drum untuk kemudian dipisahkan dari water dan dipompakan
ke Skim Oil Drum. Sedangkan gas dari stripping column degassing drum mengalir ke Vent Gas
Absorber untuk dikontakkan dengan lean amine (MEA, MDEA, DGA, atau lainnya) untuk di-absorb
H2S nya. Off gas dari Vent Gas Absorber kemudian dikirim ke Thermal Oxidizer yang ada di
Sulphur Recovery Unit untuk di-burn. Sedangkan Rich Amine (amine yang mengandung banyak
H2S) keluar dari bottom vent gas absorber dan kemudian dialirkan ke Amine Regeneration Unit
(ARU) untuk diregenerasi amine-nya. Di ARU, H2S yang keluar di top Amine Regenerator dialirkan
ke Sulphur Recovery Unit untuk di-recover sulphur-nya.

* Minyak

Minyak yang terkandung di dalam feed dipisahkan dari water berdasarkan perbedaan berat jenis.
Minyak yang mempunyai berat jenis lebih ringan daripada water akan berada pada lapisan atas/di
permukaan water pada level degassing drum. Minyak ini (biasa disebut skimmed oil) kemudian
dialirkan ke Skim Oil Drum untuk kemudian dipompakan ke Slop Oil Tank. Slop Oil yang ada di
Slop Oil tank ini selanjutnya dapat di-blending dengan Crude Oil untuk diumpankan ke Unit Crude
Distillation Unit (3-5% total feed CDU) atau di-blending dan dijual sebagai Low Sulphur Waxy
Residue/LSWR atau sebagai Fuel Oil (dapat digunakan sendiri sebagai bahan bakar fired heater
atau dijual).

* Water

Water kemudian dialirkan ke preheater (feed/product heat exchanger) sebelum kemudian menuju
SWS Column.

Tekanan degassing drum didisain cukup rendah agar kandungan H2S dan hydrocarbon ringan
(yang mudah menguap) dari feed sour water dapat ter-flash off. Biasanya tekanan degassing drum
sekitar 0,5 kg/cm2g.

1. SWS Column

Temperatur top SWS column diatur sehingga diperoleh kandungan H2S dan NH3 dalam stripped
water yang sesuai dengan spesifikasi. Sour gas dari top SWS column dikondensasi untuk
memisahkan air dengan acid gas. Semakin tinggi temperature top SWS column, maka semakin
banyak H2S dan NH3 yang akan teruapkan (semakin sedikit H2S dan NH3 yang terlarut dalam
stripped water; kualitas stripped water semakin bagus). Sebaliknya, semakin rendah temperature
top SWS column, maka semakin sedikit H2S dan NH3 yang akan ter-strip. Namun, temperatur top
SWS column dibatasi tidak boleh lebih rendah daripada 82 oC yang akan menyebabkan sublimasi
ammonium hydrosulfide (NH4HS) yang dapat menyebabkan plugging di bagian atas SWS column.

"Apakah drain line yang dari stripping tower perlu diperhatikan betul2 untuk produk H2S nya?"
Bukan Cuma H2S nya saja yang harus diperhatikan tapi juga NH3 dan Oil content-nya. Di plant
saya sekarang di Rabigh, KSA, spesifikasi kandungan H2S dan NH3 dalam Stripped Water
product (bottom SWS column) berturut-turut adalah maksimum 10 dan 30 ppmwt (untuk mencapai
target air buangan Sulfida maximum 1 ppm dan nitrogen maksimum 10 ppm). Oil content dibatasi
agar air buangan WWTP mengandung mempunyai oil content maksimum 25 ppm. Dari SWS,
stripped water masih dikirim ke WWTP untuk diolah lebih lanjut sebelum di buang ke perairan.

Sedangkan jika dalam feed SWS ada kandungan phenol, maka kandungan phenol ini gak bisa
diapa-apain oleh SWS (alias numpang lewat doang), jadi terpaksa menyerahkan sepenuhnya
penanganan phenol ini kepada bioseparator/biotreatment untuk diolah phenolnya sehingga
kandungannya bisa < 1 ppm.

WWTP biasanya terdiri dari oil separator dan biotreatment. Metode yang umum digunakan di oil
separator adalah pemisahan secara gravity menggunakan oil skimmer API/TPI. Sedangkan tugas
biotreatment adalah menurunkan kandungan organic, COD, BOD, dan phenol dengan bantuan
bakteri.

Kalo di Indonesia, BML (Baku Mutu Lingkungan) air buangan adalah sebagai berikut :

* pH = 6-9.

* Kandungan sulfida maksimum = 1 ppm.

* Kandungan ammonia maksimum = 10 ppm.

* Kandungan phenol maksimum = 1 ppm.

* Kandungan minyak maksimum = 25 ppm.

* BOD maksimum = 100 ppm.

* COD maksimum = 200 ppm.

* Temperatur maksimum = 45 oC.

Sedangkan untuk standar international, standar air buangan/effluent dari petroleum industry yang
ditetapkan oleh World Bank (Lha kok World Bank punya standar kayak gituan? Iya, World Bank
merasa perlu punya standar tersebut terkait dengan pinjaman uang kepada suatu proyek, agar
proyek tersebut tetep ramah lingkungan. Lha kenapa juga yang diambil standar-nya World Bank?
Iya, cuman itu yang saya tau):

* pH = 6-9

* BOD = 30

* COD = 150
* Oil and grease = 10

* Total Suspended Solid = 30

* Chromium Hexavalent = 0.1

* Chromium Total = 0.5

* Lead = 0.1

* Nitrogen total = 30

* Phenols = 0.5

* Benzene = 0.05

* Sulphide = 1

Ini diskusi dari pak Tigor, pak Amin dan pak Adhi juga:

Saya mau menanyakan tentang

1. Apakah perlu untuk memasang ON-LINE MONITORING untuk kualitas dumping water dari
Waste Water Treatment Plant di Oil and Gas Facility?

Kalaupun memang perlu, apakah ada industrial standard yang mengatur tentang hal ini?

Perlu tidaknya tergantung kepada seberapa konservatif kompeni Anda menerapkan aturan.
Kebetulan saya pernah terlibat dalam project seperti itu.
Namun karena alatnya mahal, ndak jadi dipasang. Rencananya akan dipasang ke unit shutdown,
jika ppmnya melebihi batas atas, WTU akan shutdown.

Standard? Itu tergantung regulasi (biasanya tergantung negara) seberapa ppm maksimal yang
bisa di dumping, misalnya 25 atau 50 ppm. Standard harus masang online monitoring sendiri saya
belum pernah lihat, tetapi standard yang mensyaratkan harus memenuhi maksimal overboard ppm
ya regulasi negara atau kompeni masing2.

Coba cek di API Standard PUBL 421 (Management of Water Discharges). Sekilas saya baca sih
kayaknya gak ada tuh keharusan masang on-line monitoring di outlet WWTP.

biasanya dipasangi

1. open channel flow meter

2. PH analizer indikator

3. level indikator utk bak penampung
4. oksigen terlarut analizer

5. yg lain sesuai kebutuhan

Kalau Pak Harry berprofesi di Drilling , saya mau tanyakan sesuatu tentang penanganan Waste
Material of Drilling activities (maklum saya awam in Drilling) :

1. Apa sajakah itu ?

RHE:

Drilling termasuk aktivitas yang secara langsung menggunakan materials yang berpotensi
menghasilkan dan atau melibatkan waste (limbah) sehingga perlu di managed dengan benar.
Sebab jika tidak, impact nya bisa runyam buat lingkungan di sekitarnya – baik untuk onshore
maupun untuk offshore
operations.

Drilling Waste itu apa aja sih?

Ya bisa berupa solid waste (semua barang padat yang tercemar hydrocarbon atau chemicals: drill
cuttings, drum, pallet, karung / sacks, dsb), produced or used fluids (sisa2 hydrocarbon, lubricants,
drilling mud, chemicals, dsb) dan emisi (emisi yang terjadi pada saat well test, pembakaran fuel di
prime movers & cranes, dsb).

2.Bagaimana menyimpan, mengangkut dan mengolah waste material ini ?

RHE:

Untuk waste management itu umumnya mengacu pada prosedur2 di ISO-14001 EMS
(environmental management systems) baik untuk solid waste, cairan maupun emisi, walaupun
tidak semua pihak melaksanakannya. On top of that, setiap drilling material biasanya dilengkapi
dengan MSDS (Material Safety Data Sheet) yang berisi keterangan mengenai produk ybs, cara2
menyimpan, mengangkut, dan meng-handle-nya, termasuk PPE yang diperlukan serta hazards vs
risks dari produk tsb.

- Untuk solid waste, biasanya ada kontainer khusus yang terbagi lagi menjadi
3: hazardous materials (mengandung pollutant, medical waste termasuk dalam
kategori ini), non-hazardous non-organic (kaca, plastik, karet) serta
non-hazardous organic (biodegradable materials). Untuk operasi drilling di
offshore, kapal2 penyangkut drilling waste pun harus memiliki permit
tersendiri.

- Untuk waste yang berupa cairan, yang terbanyak tentu dari limbah drilling mud. Oleh karena itu
sejak awal, kita mesti tentukan jenis mud yang tidak mengandung hydrocarbon dan tidak
mengandung logam berat, sehingga water based mud menjadi lebih sering dipakai. Kalaupun
kondisi sumur memerlukan penggunaan oil based mud, biasanya kita sekarang pake yang
synthetic (agak mahal memang). Impactnya terhadap sifat pollutant di drill cuttings pun bisa di
minimized dan untuk mengontrol pemakaiannya di lapangan bisa di lakukan toxicity dan LC50 test
untuk meyakinkan bahwa kita masih dalam batas baku mutu atau tidak. Untuk onshore drilling,
biasanya limbah cair ini ditampung dulu di shale pit (yang dilapisi seperti bahan plastic kedap air
agar tidak mencemari air tanah), setelah itu dialirkan ke 2-3 treatment pit untuk dinetralisir sebelum
dilepas ke saluran bebas. Untuk offshore drilling, biasanya dibuat "dripping pan" di bawah rig floor
untuk mengurangi ceceran2 lumpur yang jatuh ke permukaan laut di bawahnya. Di negara2 yang
peraturannya sangat ketat di bidang lingkungan (contohnya Alaska), umumnya limbah cair ini di
inject ke perut bumi melalui annulus di sumur2 injection, terutama ke formasi2 porous yang non-
productive sebagai final target zone.
Ada juga Operator di Indonesia yang mengumpulkan limbah cair yang berbasis hydrocarbon untuk
dicampurkan kembali bersama2 crude oil yang diproduksikan melalui production header,
sedangkan limbah cair yang mengandung bahan2 kimia lain dikumpulkan di drum2 untuk dibuang
melalui PPLI di Cileungsi Bogor.

- Untuk limbah yang berupa emisi, biasanya Operator2 kelas dunia sudah mulai meminimize well
testing dengan membakar crude oil dan atau gas di atmosfir terbuka. Untuk mereka yang ngikutin
ISO-14001, emisi yang keluar dari exhaust gen-set, crane maupun kendaraan berbahan bakar fosil
pun biasanya mereka ukur agar tidak melebihi target (dalam CO2 equivalent) yang mereka
canangkan setiap tahun.

3. Apakah ada dari pengalaman anda Waste yang mengandung Radioactive ?

RHE:

Dalam operasi drilling, memang ada alat2 electric logging yang menggunakan radioactive, tapi alat
electric logging yang menghasilkan radioactive waste saya kok gak yakin, kecuali bila alat logging
itu memang lost in hole dan gagal dipancing, sehingga dia menjadi "radioactive waste" yang harus
dilaporkan ke pihak yang berwajib (BATAN?), apalagi bila ada effect nya ke aquifer (sumber air
bersih).

4. Bagaimana pula caranya - sesuai dengan point 2 di atas ?

RHE:

Setau saya, yang namanya "radioactive source" tentu sangat berbahaya sehingga memerlukan
prosedur penyimpanan, pengangkutan dan handling yang khusus pula. Di drilling rig, radioactive
source disimpan di box khusus yang terbuat dari Pb (timah hitam) dengan ketebalan tertentu
(biasanya di cat kuning dengan tanda radioactve) dan di taruh di tempat yang cukup jauh dari
akomodasi atau dari tempat lalu lalangnya pekerja. Biar lebih afdol, saya minta Moderator KBK
"Bor" yang lain (Bung Doddy Samperuru dan Bung Ridwan – Schlumberger) untuk
menjelaskannya dengan lebih detail, sebab electric logging tools ini memang "barang mainan"
mereka sehari-hari. Monggo Mas ..... J

Tambahan :

5. Apakah Drilling termasuk aktivitas yang perlu dilengkapi AMDAL ?
RHE:

Yes, terutama untuk sumur2 pengembangan yang merupakan bagian dari POD keseluruhan.

6. Apakah tidak cukup hanya UKL/UPL ?

RHE:

UKL/UPL cukup untuk sumur2 eksplorasi.

7. Bagaimana jika drilling itu harus membuat perobahan pada dimensi,bentuk, ukuran muara
sungai e.g. dredging/pelebaran/pendalaman? Apakah perlu izin khusus dari DepHubLa untuk hal
ini ? Apakah perlu UPL/UKL khusus atau hanya menambah scope yang sudah ada ?

RHE:
Semua perubahan beserta kemungkinan dampaknya seharusnya tercakup di dalam dokumen
Amdal. Yes, bila ada dampak terhadap lalu lintas perairan, DepHubLa perlu dilibatkan. I don't think
UPL/UKL khusus diperlukan, tetapi penambahan scope bisa dilakukan dengan melalui prosedur
approval yang normal.

Untuk artikel pengertian WTP secara umum adalah: (note: disarikan dari sumber bebas (open/free
source) di wikipedia, hak cipta tetap pada narrator). Sewage treatment From Wikipedia, the free
encyclopedia

Jump to: navigation<http://en.wikipedia.org/wiki/Sewage_treatment#column-one%23column-one>,
search<http://en.wikipedia.org/wiki/Sewage_treatment#searchInput%23searchInput>

*Sewage treatment*, or *domestic wastewater treatment*, is the process of removing contaminants
<http://en.wikipedia.org/wiki/Contaminants>          from        wastewater,         both      runoff
http://en.wikipedia.org/wiki/Runoff (effluents<http://en.wikipedia.org/wiki/Effluents>) and domestic.
It includes physical, chemical and biological processes to remove physical, chemical and biological
contaminants. Its objective is to produce a waste stream (or treated
effluent<http://en.wikipedia.org/wiki/Effluent>)     and      a     solid     waste      or   sludge
<http://en.wikipedia.org/wiki/Sludge> suitable for discharge or reuse back into the environment.
This        material      is       often       inadvertently      contaminated         with    many
toxic<http://en.wikipedia.org/wiki/Toxic>organic and inorganic compounds.

Sewage is created by residences, institutions, hospitals and commercial and industrial
establishments. It can be treated close to where it is created (in septic tanks
<http://en.wikipedia.org/wiki/Septic_tank>,         biofilters<http://en.wikipedia.org/wiki/Biofilters>or
aerobic treatment systems <http://en.wikipedia.org/wiki/Aerobic_treatment_system>), or collected
and transported via a network of pipes and pump stations to a municipal treatment plant (see
sewerage<http://en.wikipedia.org/wiki/Sewerage>and                         pipes                      and
infrastructure<http://en.wikipedia.org/wiki/Sewage_collection_and_disposal>). Sewage collection
and treatment is typically subject to local, state and federal regulations and standards. Industrial
sources of wastewater often require specialized treatment processes (see Industrial wastewater
treatment<http://en.wikipedia.org/wiki/Industrial_wastewater_treatment>).

The sewage treatment involves three stages, called *primary*, *secondary*and *tertiary treatment*.
First, the solids are separated from the wastewater stream. Then dissolved biological matter is
progressively converted into a solid mass by using indigenous, water-borne
microorganisms<http://en.wikipedia.org/wiki/Microorganisms>.
Finally, the biological solids are neutralized then disposed of or re-used, and the treated water may
be disinfected chemically or physically (for example by lagoons and micro-filtration). The final
effluent can be discharged into a stream <http://en.wikipedia.org/wiki/Stream>,
river<http://en.wikipedia.org/wiki/River>,            bay             <http://en.wikipedia.org/wiki/Bay>,
lagoon<http://en.wikipedia.org/wiki/Lagoon>or wetland <http://en.wikipedia.org/wiki/Wetland>, or it
can be used for the irrigation <http://en.wikipedia.org/wiki/Irrigation> of a golf course, green way or
park. If it is sufficiently clean, it can also be used for groundwater
<http://en.wikipedia.org/wiki/Groundwater> recharge.

Description

Raw                   influent               (sewage)                 includes                household
waste<http://en.wikipedia.org/wiki/Household_waste>liquid                     from                toilets
<http://en.wikipedia.org/wiki/Toilet>,       baths<http://en.wikipedia.org/wiki/Bathing>,       showers
<http://en.wikipedia.org/wiki/Shower>,         kitchens<http://en.wikipedia.org/wiki/Kitchen>,     sinks
<http://en.wikipedia.org/wiki/Sink>, and so forth that is disposed of via sewers
<http://en.wikipedia.org/wiki/Sewer>. In many areas, sewage also includes liquid waste from
industry and commerce. The draining of household waste into greywater
<http://en.wikipedia.org/wiki/Greywater>                                                            and
blackwater<http://en.wikipedia.org/wiki/Blackwater_(waste)>is becoming more common in the
developed world, with greywater being permitted to be used for watering plants or recycled for
flushing toilets. A lot of sewage also includes some surface water from roofs or hard-standing
areas. Municipal wastewater therefore includes residential, commercial, and industrial liquid waste
discharges, and may include stormwater<http://en.wikipedia.org/wiki/Stormwater>runoff. Sewage
systems capable of handling stormwater are known as combined systems or combined sewers
<http://en.wikipedia.org/wiki/Combined_sewer>. Such systems are usually avoided since they
complicate and thereby reduce the efficiency of sewage treatment plants owing to their seasonality.
The variability in flow also leads to often larger than necessary, and subsequently more expensive,
treatment facilities. In addition, heavy storms that contribute more flows than the treatment plant
can handle may overwhelm the sewage treatment system, causing a spill or overflow (called a
combined
sewer overflow, or CSO, in the United States<http://en.wikipedia.org/wiki/United_States>).
It is preferable to have a separate storm drain<http://en.wikipedia.org/wiki/Storm_drain>system for
stormwater in areas that are developed with sewer systems.

As rainfall runs over the surface of roofs and the ground, it may pick up various contaminants
including      soil     <http://en.wikipedia.org/wiki/Soil>particles    and       other  sediment
<http://en.wikipedia.org/wiki/Sediment>, heavy metals<http://en.wikipedia.org/wiki/Heavy_metals>,
organic compounds <http://en.wikipedia.org/wiki/Organic_compound>, animal waste, and oil
<http://en.wikipedia.org/wiki/Oil> and grease<http://en.wikipedia.org/wiki/Petroleum>.
Some jurisdictions <http://en.wikipedia.org/wiki/Jurisdiction> require stormwater to receive some
level of treatment before being discharged directly into waterways. Examples of treatment
processes           used       for        stormwater       include      sedimentation       basins,
wetlands<http://en.wikipedia.org/wiki/Constructed_wetland>, buried concrete vaults with various
kinds of filters, and vortex separators (to remove coarse solids).

The site where the raw wastewater is processed before it is discharged back to the environment is
called a wastewater treatment plant (WWTP). The order and types of mechanical, chemical and
biological systems that comprise the wastewater treatment plant are typically the same for most
developed countries:

- *Mechanical treatment*
- Influx (Influent)
- Removal of large objects
- Removal of sand and grit
- Pre-precipitation
- *Biological treatment*
- Oxidation bed (oxidizing bed) or aeration<http://en.wikipedia.org/wiki/Aeration>system
- Post precipitation
- *Chemical treatment* (this step is usually combined with settling and other processes to remove
solids, such as filtration. The combination is referred to in the U.S. as physical chemical treatment.

Primary treatment removes the materials that can be easily collected from the raw wastewater and
disposed of. The typical materials that are removed during primary treatment include fats, oils, and
greases (also referred to as FOG), sand <http://en.wikipedia.org/wiki/Sand>, gravels and rocks
(also referred to as grit), larger settleable solids and floating materials (such as rags and flushed
feminine hygiene products). This step is done entirely with machinery.

Removal of large objects from influent sewage

In primary treatment, the influent sewage water is strained to remove all large objects that are
deposited in the sewer system, such as rags<http://en.wikipedia.org/wiki/Cloth>, sticks, tampons
<http://en.wikipedia.org/wiki/Tampon>,          cans<http://en.wikipedia.org/wiki/Tin_can>,   fruit
<http://en.wikipedia.org/wiki/Fruit>, etc. This is most commonly done with a manual or automated
mechanically raked bar screen. The raking action of a mechanical bar screen is typically paced
according to the accumulation on the bar screens and/or flow rate. The bar screen is used because
large solids can damage or clog the equipment used later in the sewage treatment plant. The
solids are collected in a dumpster and later disposed in a landfill.

Primary treatment also typically includes a sand or grit channel or chamber where the velocity of
the incoming wastewater is carefully controlled to allow sand grit and stones to settle, while
keeping the majority of the suspended organic material in the water column. This equipment is
called a degritter or sand catcher. Sand, grit, and stones need to be removed early in the process
to avoid damage to pumps <http://en.wikipedia.org/wiki/Pump>and other equipment in the
remaining treatment stages. Sometimes there is a sand washer (grit classifier) followed by a
conveyor that transports the sand to a container for disposal. The contents from the sand catcher
may be fed into the incinerator in a sludge processing plant, but in many cases, the sand and grit is
sent to a landfill<http://en.wikipedia.org/wiki/Landfill>.

Sedimentation

Many plants have a sedimentation stage where the sewage is allowed to pass slowly through large
tanks, commonly called "primary clarifiers" or "primary sedimentation tanks". The tanks are large
enough that sludge can settle and floating material such as grease and oils can rise to the surface
and be skimmed off. The main purpose of the primary clarification stage is to produce both a
generally homogeneous liquid capable of being treated biologically and a sludge that can be
separately treated or processed. Primary settling tanks are usually equipped with mechanically
driven scrapers that continually drive the collected sludge towards a hopper in the base of the tank
from where it can be pumped to further sludge treatment stages.

Secondary treatment

*Secondary treatment* is designed to substantially degrade the biological content of the sewage
such as are derived from human waste, food waste, soaps and detergent. The majority of
municipal and plants treat the settled sewage liquor using aerobic biological processes. For this to
be effective, the biota require both oxygen <http://en.wikipedia.org/wiki/Oxygen> and a substrate
on which to live. There are number of ways in which this is done.
In all these methods, the bacteria <http://en.wikipedia.org/wiki/Bacteria>and protozoa
<http://en.wikipedia.org/wiki/Protozoa> consume biodegradable soluble organic contaminants (e.g.
sugars<http://en.wikipedia.org/wiki/Sugar>, fats, organic short-chain carbon molecules, etc.) and
bind much of the less soluble fractions into floc <http://en.wikipedia.org/wiki/Flocculation>.
Secondary treatment systems are classified as *fixed film* or suspended growth. Fixed-film
treatment process including trickling filter<http://en.wikipedia.org/wiki/Trickling_filter>and rotating
biological     contactors<http://en.wikipedia.org/wiki/Rotating_biological_contactors>where         the
biomass grows on media and the sewage passes over its surface. In *suspended growth
systems*—such as activated sludge—the biomass is well mixed with the sewage and can be
operated in a smaller space than fixed-film systems that treat the same amount of water. However,
fixed-film systems are more able to cope with drastic changes in the amount of biological material
and can provide higher removal rates for organic material and suspended solids than suspended
growth systems.

Roughing filters <http://en.wikipedia.org/wiki/Roughing_filter> are intended to treat particularly
strong or variable organic loads, typically industrial, to allow them to then be treated by
conventional secondary treatment processes. Characteristics include typically tall, circular filters
filled with open synthetic filter media to which wastewater is applied at a relatively high rate. They
are designed to allow high hydraulic loading and a high flow-through of air. On larger installations,
air is forced through the media using blowers. The resultant wastewater is usually within the normal
range for conventional treatment processes.

<http://en.wikipedia.org/wiki/Image:Activated_Sludge_1.png>

<http://en.wikipedia.org/wiki/Image:Activated_Sludge_1.png>
A generalized, schematic diagram of an activated sludge process.

Activated sludge

*Main article: Activated sludge<http://en.wikipedia.org/wiki/Activated_sludge>
*

In general, activated sludge plants encompass a variety of mechanisms and processes that use
dissolved oxygen to promote the growth of biological floc that substantially removes organic
material.

The process traps particulate material and can, under ideal conditions, convert ammonia
<http://en.wikipedia.org/wiki/Ammonia> to nitrite<http://en.wikipedia.org/wiki/Nitrite>and nitrate
<http://en.wikipedia.org/wiki/Nitrate>              and               ultimately                   to
nitrogen<http://en.wikipedia.org/wiki/Nitrogen>gas,       (see         also           denitrification
<http://en.wikipedia.org/wiki/Denitrification>).
Surface-aerated basins

<http://en.wikipedia.org/wiki/Image:Surface-Aerated_Basin.png>

<http://en.wikipedia.org/wiki/Image:Surface-Aerated_Basin.png>

A Typical Surface-Aerated Basin (using motor-driven floating aerators)

*Main article: Aerated lagoon <http://en.wikipedia.org/wiki/Aerated_lagoon>*

Most biological oxidation processes for treating industrial wastewaters have in common the use of
oxygen (or air) and microbial action. Surface-aerated basins achieve 80 to 90% removal of
Biochemical Oxygen Demand<http://en.wikipedia.org/wiki/Biochemical_Oxygen_Demand>with
retention times of 1 to 10 days.

In an aerated basin system, the aerators provide two functions: they transfer air into the basins
required by the biological oxidation reactions, and they provide the mixing required for dispersing
the air and for contacting the reactants (that is, oxygen, wastewater and microbes). Typically, the
floating surface aerators are rated to deliver the amount of air equivalent to 1.8 to 2.7 kg

Biological oxidation processes are sensitive to temperature and, between 0°C and 40 °C, the rate
of biological reactions increase with temperature. Most surface aerated vessels operate at between
4 °C and 32°C.[1]<http://en.wikipedia.org/wiki/Sewage_treatment#cite_note-Basin-0%23cite_note-
Basin-0>
Fluidized bed reactors

The carbon absorption following biological treatment is particularly effective in reducing both the
BOD and COD to low levels. A fluidized bed reactor is a combination of the most common stirred
tank packed bed, continuous flow reactors. It is very important to chemical engineering because of
its excellent heat and mass transfer characteristics. In a fluidized bed reactor, the substrate is
passed upward through the immobilized enzyme bed at a high velocity to lift the particles. However
the velocity must not be so high that the enzymes are swept away from the reactor entirely. This
causes low mixing; these type of reactors are highly suitable for the exothermic reactions. It is most
often applied in
immobilized enzyme catalysis Filter beds (oxidising beds)

*Main article: Trickling filter<http://en.wikipedia.org/wiki/Trickling_filter>
*

In      older     plants     and      plants       receiving   more    variable     loads,    trickling
filter<http://en.wikipedia.org/wiki/Trickling_filter>beds are used where the settled sewage liquor is
spread onto the surface of a deep bed made up of coke
<http://en.wikipedia.org/wiki/Coke_(fuel)>(carbonised                  coal),               limestone
<http://en.wikipedia.org/wiki/Limestone> chips or specially fabricated plastic media. Such media
must have high surface areas to support the biofilms that form. The liquor is distributed through
perforated rotating arms radiating from a central pivot. The distributed liquor trickles through this
bed and is collected in drains at the base. These drains also provide a source of air which
percolates up through the bed, keeping it aerobic. Biological films of bacteria, protozoa and fungi
form on the media's surfaces and eat or otherwise reduce the organic content. This biofilm
<http://en.wikipedia.org/wiki/Biofilm> is grazed by insect larvae and worms which help maintain an
optimal thickness. Overloading of beds increases the thickness of the film leading to clogging of the
filter media and ponding on the surface.

Biological aerated filters

Biological Aerated (or Anoxic) Filter (BAF) or Biofilters combine filtration with biological carbon
reduction, nitrification<http://en.wikipedia.org/wiki/Nitrification>or denitrification. BAF usually
includes a reactor filled with a filter <http://en.wikipedia.org/wiki/Filter_(water)> media. The media is
either in suspension or supported by a gravel layer at the foot of the filter. The dual purpose of this
media is to support highly active biomass that is attached to it and to filter suspended solids.
Carbon reduction and ammonia conversion occurs in aerobic mode and sometime achieved in a
single         reactor             while           nitrate         conversion           occurs         in
anoxic<http://en.wikipedia.org/wiki/Hypoxia_(environmental)>mode. BAF is operated either in
upflow or downflow configuration depending on design specified by manufacturer.

Membrane bioreactors

Membrane bioreactors
<http://en.wikipedia.org/wiki/Membrane_bioreactor>(MBR) combines activated sludge treatment
with a membrane liquid-solid separation process. The membrane component uses low pressure
microfiltration or ultra filtration membranes and eliminates the need for clarification and tertiary
filtration. The membranes are typically immersed in the aeration tank (however, some applications
utilize a separate membrane tank). One of the key benefits of a membrane
bioreactor<http://en.wikipedia.org/wiki/Membrane_bioreactor>system is that it effectively
overcomes the limitations associated with poor settling of sludge in conventional activated
sludge<http://en.wikipedia.org/wiki/Activated_sludge>(CAS) processes.
The technology permits bioreactor operation with considerably higher mixed liquor suspended
solids (MLSS) concentration than CAS systems, which are limited by sludge settling. The process
is typically operated at MLSS in the range of 8,000–12,000 mg/L, while CAS are operated in the
range of 2,000–3,000 mg/L. The elevated biomass concentration in the membrane bioreactor
<http://en.wikipedia.org/wiki/Membrane_bioreactor> process allows for very effective removal of
both soluble and particulate biodegradable materials at higher loading rates. Thus increased
Sludge Retention Times (SRTs)—usually exceeding 15 days—ensure complete nitrification even in
extremely cold weather.

The cost of building and operating a MBR is usually higher than conventional wastewater
treatment, however, as the technology has become increasingly popular and has gained wider
acceptance throughout the industry, the life-cycle costs have been steadily decreasing. The small
footprint of MBR systems, and the high quality effluent produced, makes them particularly useful
for water reuse applications.

Secondary sedimentation

The final step in the secondary treatment stage is to settle out the biological floc or filter material
and produce sewage water containing very low levels of organic material and suspended matter.

Rotating biological contactors

*Main article: Rotating biological
contactor<http://en.wikipedia.org/wiki/Rotating_biological_contactor>
*

<http://en.wikipedia.org/wiki/Image:Rotating_Biological_Contactor.png>

<http://en.wikipedia.org/wiki/Image:Rotating_Biological_Contactor.png>

Schematic diagram of a typical rotating biological contactor (RBC). The treated effluent
clarifier/settler is not included in the diagram.

Rotating biological contactors (RBCs) are mechanical secondary treatment systems, which are
robust and capable of withstanding surges in organic load. RBCs were first installed in
Germany<http://en.wikipedia.org/wiki/Germany>in 1960 and have since been developed and
refined into a reliable operating unit. The rotating disks support the growth of bacteria and micro-
organisms present in the sewage, which breakdown and stabilise organic pollutants. To be
successful, micro-organisms need both oxygen to live and food to grow. Oxygen is obtained from
the atmosphere as the disks rotate. As the micro-organisms grow, they build up on the media until
they are sloughed off due to shear forces provided by the rotating discs in the sewage. Effluent
from the RBC is then passed through final clarifiers where the micro-organisms in suspension
settle as a sludge. The sludge is withdrawn from the clarifier for further treatment.

A functionally similar biological filtering system has become popular as part of home aquarium
<http://en.wikipedia.org/wiki/Aquarium> filtration and purification. The aquarium water is drawn up
out of the tank and then cascaded over a freely spinning corrugated fiber-mesh wheel before
passing through a media filter and back into the aquarium. The spinning mesh wheel develops a
biofilm <http://en.wikipedia.org/wiki/Biofilm> coating of microorganisms that feed on the suspended
wastes in the aquarium water and are also exposed to the atmosphere as the wheel rotates. This is
especially good at removing waste urea and ammonia urinated into the aquarium water by the fish
and other animals.

Tertiary treatment

Tertiary treatment provides a final stage to raise the effluent quality before it is discharged to the
receiving environment (sea, river, lake, ground, etc.). More than one tertiary treatment process may
be used at any treatment plant. If disinfection is practiced, it is always the final process. It is also
called "effluent polishing".

Filtration

Sand filtration <http://en.wikipedia.org/wiki/Sand_filter> removes much of the residual suspended
matter. Filtration over activated carbon<http://en.wikipedia.org/wiki/Activated_carbon>removes
residual toxins <http://en.wikipedia.org/wiki/Toxin>.

Lagooning

Lagooning provides settlement and further biological improvement through storage in large man-
made ponds or lagoons. These lagoons are highly aerobic and colonization by native
macrophytes<http://en.wikipedia.org/wiki/Macrophyte>, especially reeds, is often encouraged.
Small filter feeding invertebrates<http://en.wikipedia.org/wiki/Invertebrate>such as
Daphnia             <http://en.wikipedia.org/wiki/Daphnia>            and         species   of
Rotifera<http://en.wikipedia.org/wiki/Rotifera>greatly assist in treatment by removing fine
particulates.

Constructed wetlands

Constructed wetlands
<http://en.wikipedia.org/wiki/Constructed_wetland>include           engineered            reedbeds
<http://en.wikipedia.org/wiki/Reedbed> and a range of similar methodologies, all of which provide a
high degree of aerobic biological improvement and can often be used instead of secondary
treatment              for           small           communities,              also             see
phytoremediation<http://en.wikipedia.org/wiki/Phytoremediation>.
One example is a small reedbed used to clean the drainage from the
elephants<http://en.wikipedia.org/wiki/Elephant>'      enclosure        at       Chester       Zoo
<http://en.wikipedia.org/wiki/Chester_Zoo> inEngland <http://en.wikipedia.org/wiki/England>.

Nutrient removal

Wastewater          may         contain        high      levels        of       the        nutrients
nitrogen<http://en.wikipedia.org/wiki/Nitrogen>and
phosphorus <http://en.wikipedia.org/wiki/Phosphorus>. Excessive release to the environment can
lead to a build up of nutrients, called eutrophication<http://en.wikipedia.org/wiki/Eutrophication>,
which can in turn encourage the overgrowth of weeds, algae<http://en.wikipedia.org/wiki/Algae>,
and cyanobacteria <http://en.wikipedia.org/wiki/Cyanobacteria> (blue-green algae). This may
cause an algal bloom<http://en.wikipedia.org/wiki/Algal_bloom>, a rapid growth in the population of
algae. The algae numbers are unsustainable and eventually most of them die. The decomposition
of the algae by bacteria uses up so much of oxygen in the water that most or all of the animals die,
which creates more organic matter for the bacteria to decompose. In addition to causing
deoxygenation, some algal species produce toxins that contaminate drinking
water<http://en.wikipedia.org/wiki/Drinking_water>supplies. Different treatment processes are
required to remove nitrogen and phosphorus.

Nitrogen removal

The        removal       of      nitrogen        is     effected         through       the      biological
oxidation<http://en.wikipedia.org/wiki/Redox>of              nitrogen            from           ammonia
http://en.wikipedia.org/wiki/Ammonia (nitrification<http://en.wikipedia.org/wiki/Nitrification>)
to       nitrate     <http://en.wikipedia.org/wiki/Nitrate>,        followed        by      denitrification
<http://en.wikipedia.org/wiki/Denitrification>, the reduction of nitrate to nitrogen gas. Nitrogen gas is
released to the atmosphere and thus removed from the water.

Nitrification itself is a two-step aerobic process, each step facilitated by a different type of bacteria.
The oxidation of ammonia (NH3) to nitrite (NO2−) is most often facilitated by *Nitrosomonas* spp.
(nitroso referring to the formation of a nitroso <http://en.wikipedia.org/wiki/Nitroso> functional
group). Nitrite oxidation to nitrate (NO3−), though traditionally believed to be facilitated by
*Nitrobacter* spp. (nitro referring the formation of a nitro functional group
<http://en.wikipedia.org/wiki/Nitro_functional_group>), is now known to be facilitated in the
environment almost exclusively by *Nitrospira* spp.

Denitrification requires anoxic conditions to encourage the appropriate biological communities to
form. It is facilitated by a wide diversity of bacteria. Sand filters, lagooning and reed beds can all be
used to reduce nitrogen, but the activated sludge process (if designed well) can do the job the most
easily. Since denitrification is the reduction of nitrate to dinitrogen gas, an electron
donor<http://en.wikipedia.org/wiki/Electron_donor>is needed. This can be, depending on the
wastewater, organic matter (from faeces), sulfide <http://en.wikipedia.org/wiki/Sulfide>, or an
added donor like methanol <http://en.wikipedia.org/wiki/Methanol>.

Sometimes the conversion of toxic ammonia to nitrate alone is referred to as tertiary treatment.

Nitrogen removal is important for treatment plants such as in NYC where the final effluent goes into
waterways that are abundant in marine life. Nitrogen aids in the growth of plants which use oxygen
thus reducing the nuber of beneficial marine life from our waterways.

Phosphorus removal

Phosphorus can be removed biologically in a process called enhanced biological phosphorus
removal<http://en.wikipedia.org/wiki/Enhanced_biological_phosphorus_removal>. In this process,
specific bacteria, called polyphosphate accumulating organisms (PAOs), are selectively enriched
and accumulate large quantities of phosphorus within their cells (up to 20% of their mass). When
the biomass enriched in these bacteria is separated from the treated water, these biosolids have a
high fertilizer <http://en.wikipedia.org/wiki/Fertilizer>value.
Phosphorus           removal        can       also         be       achieved       by      chemical
precipitation<http://en.wikipedia.org/wiki/Precipitation_(chemistry)>,     usually    with    salts
<http://en.wikipedia.org/wiki/Salt> of iron<http://en.wikipedia.org/wiki/Iron>(e.g. ferric chloride
<http://en.wikipedia.org/wiki/Ferric_chloride>),
aluminum<http://en.wikipedia.org/wiki/Aluminum>(e.g. alum <http://en.wikipedia.org/wiki/Alum>), or
lime. The resulting chemical sludge is difficult to handle and the added chemicals can be
expensive. Despite this, chemical phosphorus removal requires significantly smaller equipment
footprint than biological removal, is easier to operate and is often more reliable than biological
phosphorus removal. This is particularly important for water reuse systems where high phosphorus
concentrations may lead to fouling of downstream equipment such as reverse
osmosis<http://en.wikipedia.org/wiki/Reverse_osmosis>
.
Disinfection

The purpose of disinfection <http://en.wikipedia.org/wiki/Disinfection> in the treatment of
wastewater         is     to  substantially       reduce    the     number       of     microorganisms
<http://en.wikipedia.org/wiki/Microorganism> in the water to be discharged back into the
environment. The effectiveness of disinfection depends on the quality of the water being treated
(e.g., cloudiness, pH, etc.), the type of disinfection being used, the disinfectant dosage
(concentration and time), and other environmental variables. Cloudy water will be treated less
successfully since solid matter can shield organisms, especially from ultraviolet
light<http://en.wikipedia.org/wiki/Ultraviolet_light>or if contact times are low. Generally, short
contact times, low doses and high flows all militate against effective disinfection. Common methods
of           disinfection        include            ozone        <http://en.wikipedia.org/wiki/Ozone>,
chlorine<http://en.wikipedia.org/wiki/Chlorine>,         or     ultraviolet      light.     Chloramine
<http://en.wikipedia.org/wiki/Chloramine>, which is used for drinking water, is not used in
wastewater treatment because of its persistence.

Chlorination <http://en.wikipedia.org/wiki/Chlorination> remains the most common form of
wastewater disinfection in North America<http://en.wikipedia.org/wiki/North_America>due to its low
cost and long-term history of effectiveness. One disadvantage is that chlorination of residual
organic material can generate chlorinated-organic compounds that may be
carcinogenic<http://en.wikipedia.org/wiki/Carcinogenic>or harmful to the environment. Residual
chlorine or chloramines may also be capable of chlorinating organic material in the natural aquatic
environment. Further, because residual chlorine is toxic to aquatic species, the treated effluent
must also be chemically dechlorinated, adding to the complexity and cost of treatment.

Ultraviolet <http://en.wikipedia.org/wiki/Ultraviolet> (UV) light can be used instead of chlorine,
iodine, or other chemicals. Because no chemicals are used, the treated water has no adverse
effect on organisms that later consume it, as may be the case with other methods. UV radiation
causes damage to the genetic <http://en.wikipedia.org/wiki/Gene> structure of bacteria, viruses
<http://en.wikipedia.org/wiki/Virus>, and other pathogens<http://en.wikipedia.org/wiki/Pathogen>,
making them incapable of reproduction. The key disadvantages of UV disinfection are the need for
frequent lamp maintenance and replacement and the need for a highly treated effluent to ensure
that the target microorganisms are not shielded from the UV radiation (i.e., any solids present in
the treated effluent may protect microorganisms from the UV light). In the United Kingdom, light is
becoming the most common means of disinfection because of the concerns about the impacts of
chlorine in chlorinating residual organics in the wastewater and in chlorinating organics in the
receiving water.
Edmonton<http://en.wikipedia.org/wiki/Edmonton>, Alberta <http://en.wikipedia.org/wiki/Alberta>,
Canada also uses UV light for its water treatment.

Ozone <http://en.wikipedia.org/wiki/Ozone>
O<http://en.wikipedia.org/wiki/Oxygen>
3 is generated by passing oxygen O
<http://en.wikipedia.org/wiki/Oxygen>2through a high voltage <http://en.wikipedia.org/wiki/Voltage>
potential resulting in a third oxygen atom <http://en.wikipedia.org/wiki/Atom> becoming attached
and forming O <http://en.wikipedia.org/wiki/Oxygen>3. Ozone is very unstable and reactive and
oxidizes most organic material it comes in contact with, thereby destroying many pathogenic
microorganisms. Ozone is considered to be safer than chlorine because, unlike chlorine which has
to be stored on site (highly poisonous in the event of an accidental release), ozone is generated
onsite as needed. Ozonation also produces fewer disinfection by-products than chlorination. A
disadvantage of ozone disinfection is the high cost of the ozone generation equipment and the
requirements for special operators. Package plants and batch reactors

In order to use less space, treat difficult waste, deal with intermittent flow or achieve higher
environmental standards, a number of designs of hybrid treatment plants have been produced.
Such plants often combine all or at least two stages of the three main treatment stages into one
combined
stage. In the UK, where a large number of sewage treatment plants serve small populations,
package plants are a viable alternative to building discrete structures for each process stage.

One type of system that combines secondary treatment and settlement is the sequencing batch
reactor <http://en.wikipedia.org/wiki/Sequencing_batch_reactor> (SBR). Typically, activated sludge
is mixed with raw incoming sewage and mixed and aerated. The resultant mixture is then allowed
to settle producing a high quality effluent. The settled sludge is run off and re-aerated before a
proportion is returned to the head of the works. SBR plants are now being deployed in many parts
of the world including North Liberty, Iowa<http://en.wikipedia.org/wiki/North_Liberty,_Iowa>, and
Llanasa<http://en.wikipedia.org/w/index.php?title=Llanasa&action=edit&redlink=1>, North Wales
<http://en.wikipedia.org/wiki/North_Wales>.

The disadvantage of such processes is that precise control of timing, mixing and aeration is
required. This precision is usually achieved by computer controls linked to many sensors in the
plant. Such a complex, fragile system is unsuited to places where such controls may be unreliable,
or poorly maintained, or where the power supply may be intermittent.

Package plants may be referred to as *high charged* or *low charged*. This refers to the way the
biological load is processed. In high charged systems, the biological stage is presented with a high
organic load and the combined floc and organic material is then oxygenated for a few hours before
being charged again with a new load. In the low charged system the biological stage contains a low
organic load and is combined with floculate for a relatively long time.

Sludge treatment and disposal
*Main article: Sewage sludge
treatment<http://en.wikipedia.org/wiki/Sewage_sludge_treatment>
*

The sludges accumulated in a wastewater treatment process must be treated and disposed of in a
safe and effective manner. The purpose of digestion is to reduce the amount of organic
matter<http://en.wikipedia.org/wiki/Organic_matter>and the number of disease-causing
microorganisms <http://en.wikipedia.org/wiki/Microorganism> present in the solids. The most
common                  treatment              options            include             anaerobic
digestion<http://en.wikipedia.org/wiki/Anaerobic_digestion>,          aerobic          digestion
<http://en.wikipedia.org/wiki/Aerobic_digestion>,              and                   composting
<http://en.wikipedia.org/wiki/Composting>.

The choice of a wastewater solid treatment method depends on the amount of solids generated
and other site-specific conditions. However, in general, composting is most often applied to
smaller-scale applications followed by aerobic digestion and then lastly anaerobic digestion for the
larger-scale municipal applications.

Anaerobic digestion

*Main article: Anaerobic digestion<http://en.wikipedia.org/wiki/Anaerobic_digestion>
*

Anaerobic digestion is a bacterial process that is carried out in the absence of oxygen. The process
can either be *thermophilic<http://en.wikipedia.org/wiki/Thermophile>
*               digestion,               in               which               sludge               is
fermented<http://en.wikipedia.org/wiki/Fermentation_(biochemistry)>in
tanks at a temperature of 55°C, or *mesophilic <http://en.wikipedia.org/wiki/Mesophile>*, at a
temperature of around 36°C. Though allowing shorter retention time (and thus smaller tanks),
thermophilic digestion is more expensive in terms of energy consumption for heating the sludge.

One      major      feature      of     anaerobic  digestion  is   the    production      of
biogas<http://en.wikipedia.org/wiki/Biogas>, which can be used in generators for electricity
production and/or in boilers for heating purposes.

Aerobic digestion

Aerobic <http://en.wikipedia.org/wiki/Aerobic_organism> digestion is a bacterial process occurring
in              the              presence              of             oxygen.               Under
aerobic<http://en.wikipedia.org/wiki/Aerobic_organism>conditions,
bacteria rapidly consume organic matter and convert it into carbon dioxide
<http://en.wikipedia.org/wiki/Carbon_dioxide>. The operating costs are characteristically much
greater for aerobic digestion because of theenergy costs needed to add oxygen to the process.

Composting
Composting <http://en.wikipedia.org/wiki/Composting> is also an aerobic process that involves
mixing the sludge with sources of carbon<http://en.wikipedia.org/wiki/Carbon>such as sawdust,
straw or
wood chips. In the presence of oxygen, bacteria digest both the wastewater solids and the added
carbon source and, in doing so, produce a large amount of heat.

Sludge disposal

When a liquid sludge is produced, further treatment may be required to make it suitable for final
disposal. Typically, sludges are thickened (dewatered) to reduce the volumes transported off-site
for disposal. There is no process which completely eliminates the need to dispose of biosolids.
There is, however, an additional step some cities are taking to superheat the wastewater sludge
and convert it into small pelletized granules that are high in nitrogen and other organic materials. In
NYC, for example, several sewage treatment plants have dewatering facilities that use large
centrifuges along with the addition of chemicals such as polymer to further remove liquid from the
sludge. The removed fluid is called centrate is is typically reintroduced into the wastewater
process. The product which is left is called cake and that is picked up by companies which turn it
into fertilizer pellets. This product is then sold to local farmers and turf farms as a soil amendment
or fertilizer, reducing the amount of space required to dispose of sludge in
landfills[1]<http://www.nefcobiosolids.com/>.

Kebetulan dulu sewaktu masih di Qatar Gas 2 sempat ditugaskan di Effluent Area, jadi sedikit-
sedkit nyenggol topik ini.

Fakhri


Pak Thomas,
Saya mau tanya ttg spesifikasi benzene dan phenol dalam effluent dalam praktek di Indonesia
sbb:
1) Kira-kira benzene <0.05 ppm itu bisa dicapai hanya secara biolofycal tretament atau harus
pakai karbon aktif?
2) Saya rasa phenol mudah diturunkan ke 1 ppm secara biologi.

Thanks and regards,


Thomas Yanuar


Pak Fakhri,

Waduh, saya bukan ahli Proses nih, kebetulan bidang keahlian saya di Sipil dan Struktur serta
sebagian Project Management. Silahkan ditanyakan ke Pak Adhi Budhiarto, pakarnya dan
sekaligus KBK Proses milis kita.

adhi budhiarto
Wah rangkuman yang lengkap nih Pak Thomas. Baru aja saya mau fwd japri ke mbak Putri tulisan
saya tsb, eh udah di-response dengan rangkuman yang lebih lengkap dari Pak Thomas. Trims
Pak Thomas.

Mbak Putri, kalo mau diskusi lebih detil lagi tentang waste water treatment di kilang (terutama
SWS) boleh japri ke saya or diskusi lewat jarum juga gak masalah.

Thomas Yanuar


Hehehe...sama-sama Pak Adhi.
Dari dulu saya sudah tertarik dengan proses di WTP baik untuk O/G, Industri ataupun skala
penerapan untuk publik, meskipun saya juga masih awam lho Pak.

Teguh Santoso

Produce water treatment, baik onshore/offshore memiliki proses yang sama yaitu memisahkan air
hasil proses dari sisa minyak disuatu tempat. kalau onshore biasanya dimasukkan ke kolam
penampung (pit) sedangkan di offshore disebut coisson. minyak akan terpisah dengan sendirinya
dan akan berada di lapisan atas. atau bisa juga ditambahkan cemical untuk menarik molekul
minyak yang larut di air menjadi lapisan minyak. Di onshore lapisan minyak ini dipompa lagi oleh
pit pump. di offoshore pompa ini biasa disebut sump pump untuk mengambil kembali lapisan
minyak yang ada di coisson bagian atasnya. bedanya lagi spec pompa untuk offshore harus tahan
korosi air laut. berapa yang boleh dibuang kelaut? ukurannya sekian ppm saya lupa, maaf.
Bedanya lagi, di onshore efek lingkungan dan sosialnya lebih besar daripada di offshore.. Kalau di
onshore airnya bisa dimanfaatkan untuk lainnya misalnya untuk water injection well, dll.
Demikian, kalau ada tambahan dari yang lain atau koreksi monggo...


Fakhri


Pak Teguh and all,
Pemisahan minyak dg air dilakukan dg cara settling baik secara gravitational settling (caisson)
maupun hydrocylone settling. Kedua- duanya memamfaatkan perbedaan settling velocity karena
adanya perbedaan densitas air dengan minyak serta adanya gaya baik berupa gravitasi maupun
gaya centrifugal (cyclone).

Produced water di offshore diolah pertama-tama dg hydrocylcone kemudian dikirim ke caisson.
Menurut saya caisson tidak akan bisa lagi memisahkan minyak yg tidak terpisahkan oleh
hydrocyclone karena hydrocyclone lebih effective daripada caisson.

Tolong kalau ada yg bisa menjelaskan fungsi caisson selain untuk pemisahan di instalasi offshore.

Thanks and Regards,
Sketska Naratama


Btw,
Saya ada contoh proposal waster water treatment (Hydrocyclone) utk Offshore.
Jika mau dipersilahkan respon ke email saya pribadi. Rekan saya yang sekarang di KL cerita
bahwa PTDI sempat design dan complete installation di beberapa offshore di IND. Sayang nya
sekarang sudah tidak lagi.

Paket pekerjaan ini nilai nya cukup lumayan. Sebagai gambaran design flowrate 2400 BWPD,
10Barg dengan pack outlet oil concentration <15Ppm lengkap dgn Hydrocyclone vessel 6" 3x33%,
Flotation unit 1x100% plus aksesoris yang berhubungan on skid, bisa diatas 1Juta USD. Semoga
saja pemain nya banyak dari kita (Ind) sehingga tidak lari kemana keuntungan yang didapat. Lagi
pula tentu Local Content nya akan semakin besar dan banyak orang Ind yg bisa involve disini.

ebahagia

Pak Sketsa,

Apa system tersebut juga mengkonsumsi demulsifier chemical?

putri nora novera mindra

Terimakasih Pak Yanuar, Pak Adhi, Pak Fakhri dan Pak Naratama atas sharing ilmunya sangat
bermanfaat buat saya
Mudah2an masih ada sharing dari rekan milis lainnya ttg related topic
Saya tunggu...

				
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