anaerobic treatment process - institut teknologi...

26
ANAEROBIC TREATMENT PROCESS Marisa Handajani

Upload: phungtuong

Post on 10-Mar-2019

243 views

Category:

Documents


4 download

TRANSCRIPT

ANAEROBIC TREATMENT

PROCESSPROCESS

Marisa Handajani

Anaerobic Process

• Methane fermentation is a versatile biotechnology capable of converting almost all types of polymeric materials to methane and carbon dioxide under anaerobic conditions.

• Tahapan Proses:1. Hidrolisis

2. Asidegenesis

3. Metanogenesis3. Metanogenesis

• Microorganisms : 1. fermentative microbes (acidogens);

2. hydrogen-producing,

3. acetate-forming microbes (acetogens); and

4. methane-producing microbes (methanogens) harmoniously grow and produce reduced end-products.

• Anaerobes play important roles in establishing a stable environment at various stages of methane fermentation.

Reaksi pembentukan Metan:

4H2+CO2�CH4+2H2O

4HCOOH� CH4+3CO2+2H2O

CH3COOH �CH4+CO2

4CH3OH � 3CH4+CO2+2H2O

4(CH3)3N+H2O

�9CH4+3CO2+6H2O+4NH3

Anaerobic Wastewater Treatment:

• Anaerobic wastewater treatment is the biological treatment of wastewater without the use of air or elemental oxygen. Many applications are directed towards the removal of organic pollution in wastewater, slurries and sludges. The organic pollutants are converted by anaerobic microorganisms to a gas containing methane and carbon dioxide, known as "biogas" (see Figure 1 below). below).

Figure 1. Conversion of Organic Pollutants to Biogas by Anaerobic Microorganisms

COD Balance:In the wastewater engineering field organic pollution is measured by the weight of

oxygen it takes to oxidize it chemically. This weight of oxygen is referred to as the

"chemical oxygen demand" (COD). COD is basically a measure of organic matter

content or concentration. The best way to appreciate anaerobic wastewater treatment

is to compare its COD balance with that of aerobic wastewater treatment.

Anaerobic vs Aerobic Treatment for 1000 kg CODB/d

Parameter Anaerobic Aerobic

Power consumption (kW) 1.5 65

Net biosolids prod. (kg TS/d) 15-100 200-600

Energy produced (kW) 140 Nil

Anaerobic Process

Benefits

• Less nutrients required;

• System can be shut down

for extended periods

without serious

Disadvantages

• Anaerobic treatment cannot

achieve surface water

discharge quality without

post-treatment; without serious

deterioration; and

• Can handle organic shock

loads effectively.

post-treatment;

• Reduced sulfur compounds

are produced, which need

to be properly addressed in

terms of corrosion, odor

and safety; and

• Longer start-up period.

Anaerobic systems

• Suspended-growth processes

systems where the bacteria grow and are suspended

in the reactor liquid �'granular' or 'flocculent‘

• Attached-growth processes

utilize either fixed film or carrier media (which is

suspended in the liquid) for the bacteria to grow on

and attach to.

Application• "High Rate"Anaerobic Treatment:

SRT ≠ HRT

• Granular sludges exhibit high settling velocities and activity rates � reduce reactor volume

and increase the organic loading rate � depend on wastewater characteristics, system

configuration and loading condition

• granular sludge is retained in the system by specially designed gas-liquid-solids separation • granular sludge is retained in the system by specially designed gas-liquid-solids separation

devices,

• “Low Rate"Anaerobic Treatment:

SRT = HRT

effective when treating wastewaters that do not granulate well or have substances that

effect the retention of granules at high loading rates (i.e., high concentrations of fat, oil or

grease (FOG), total suspended solids (TSS), COD, salts, total dissolved solids, calcium, etc., in

the wastewater).

• The net effect is that slow growing anaerobes can be

maintained in the reactor at high concentrations, enabling

high volumetric conversion rates, while the wastewater

rapidly passes through the reactor.

• The main mechanism of retaining sludge in the reactor is

immobilization onto support material (microorganisms

sticking to surfaces, eg. filter material in the "anaerobic filter")

or self-aggregation into pellets (microorganisms sticking to

each other, eg. sludge granules).

Anaerobic Contact Process• This process consists of a

suspended-growth reactor, with

typical loadings in the range of 0.5

to 3 kg COD/m3/d.

• The lower volumetric loading rate

allows the reactor to retain non-

granular flocculent biomass and to

treat wastewaters that have higher

COD, TSS and FOG than can be

handled by high-rate processes. handled by high-rate processes.

• Effective for treatingwastewaters, such as potato processing, dairy and cheese,

yeast and distillery.

• The larger volume of the system means that it occupies more land area;

• Retains a large amount of biomass, which gives the process more stability and

robustness than higher rate systems.

• The system can operate at lower temperatures than other processes and

generates less waste sludge on a dry weight basis.

Upflow Anaerobic Sludge-Blanket Process

• Influent flow is typically equalized,

neutralized and partially acidified in a

separate tank ahead of the reactor.

• The influent flow is often mixed with

effluent recycle and then distributed into

the lower part of the reactor below the

sludge bed.

• The upper portion of the reactor typically

has a gas-liquid-solids separator (GLSS)

that removes biogas and clarifies the

Up flow velocity : 0.6 – 0.9 m/h

Granules range in size

from 0.5-2.5 mm,

that removes biogas and clarifies the

effluent.

UASB• UASB reactors typically require low influent TSS concentrations (< 15 percent of the influent

COD concentration) and FOG concentrations (< 100 milligram per liter (mg/l)).

• Concentration from 50-100 kg VSS/m3 at the bottom, to 5-40 kg VSS/m3 in the upper part of

the reactor.

• OLR: 5-15 kg COD/m3/d

• Significant parameters in the UASB operation are floe diameter, microbial density, and the

structure of the gas-solid separator which effectively retains the microbial granules within the

reactor. reactor.

• The criteria :

(a) selection of a suitable waste water capable of granule self-formation;

(b) operation of the reactor without mechanical agitation;

(c) start up at a relatively low COD load;

(d) use of waste water containing Ca2+ and Ba2+ and

(e) avoidance of bulking caused by filamentous microbial growth. Granule formation in a

UASB system is influenced by the growth of rod-type Methanothrix spp. which produce

spherical granules.

Anaerobic Fixed Bed Process• Rasio H/d = 1-2

• Nozzle umpan : 5 – 10 m2

• Kecepatan fluida 1-2 m/h

• Rasio resirkulasi 5-10

• Tinggi fixed bed max 7 m; keseluruhan reaktor max 14,5 m

• OLR : 5-15 kg COD/m3/d.

• used for removal of soluble organics and has similar loading • used for removal of soluble organics and has similar loading

limits in terms of FOG (< 100 mg/l) and TSS (< 15 percent of

COD) concentrations.

AnFB• Full-scale UAFP systems (waste water can be treated at an HRT of 7.8 days with 74% COD

removal. Application of this UAFP to domestic sewage treatment using Raschig rings (2.5 cm)

as microbial supports, resulted in BOD removal of 50 to 60 % and suspended solids (SS)

removal of 70 to 80%, at an HRT ranging from 5 to 33 hours.

• Selection of a medium in which microbial adhesion is greatly influenced both by SS, and the

chemical composition of the waste water, is extremely critical in UAFP systems. The effects of

physical medium characteristics, such as size and shape, on COD removal have been

investigated using modular corrugated blocks (porosity > 95%), pall rings, and perforated

spheres.

• At a COD load of 2 kg/m/day, modular corrugated blocks exhibited superior behavior,

removing 88 % of COD. A comparison of COD removal for cross- and tubular-flow systems,

reveals that COD removal is 20 to 30 % greater in cross-flow systems.

• In addition to plastic media, baked clay and a melted slug have also proven useful in

laboratory experiments on methanogenesis from formate, acetate, and methanol. Pumice

was used as a microbial supporter for methanogenesis from methanol-rich waste water of

the evaporate condensate from a pulp mill (COD load: 12 kg/m3/day, COD removal: 96%).

Expanded Bed Process (Fluidized)

• Media: Pasir, batu bara, agregat lain

• Biomassa tumbuh pada permukaan media

• Konsentrasi biomassa 15.000-40.000 mg/l

• Rasio H/d = 5 – 25

• Faktor kunci: fluidization zone � distribusi• Faktor kunci: fluidization zone � distribusi

homogen “dead zone” dan “high shear force”

• Tinggi fluidized bed ditentukan oleh flow rate

• Untuk mengurangi kehilangan media:

• “stationary support-biomass separation

device” pada tinggi bed maximum (minimum

1,5 m dibawah overflow)

• Mengatur kecepatan fluidisasi

• OLR :10 - 25 kg COD/m3/d.

AnEB• Use of artificial sewage in an AFBR, resulted in COD removal exceeding 80 % at 20°C, and at a

COD load of 2-4 kg/m3/day this system was tolerant of shock loading for step changes of

temperature from 13 to 35°C and from 35 to 13°C. In the case of COD shock loading from 1.3

to 24 kg/m3/day, a steady state is established after 6 days. The AFBR thus seems to be

capable of performing at relatively low temperatures with both low and high COD waste

waters, without significant shock loading effects.

• The AFBR has been progressively developed, as shown by the full-scale operation data in

Table 4-5. Engineering improvements which can potentially minimize the mechanical power

required for fluidization include reduction of the expanded volume, selection of a low density required for fluidization include reduction of the expanded volume, selection of a low density

medium of high specific area; and avoidance of fragility. Media such as sand, quartzite,

alumina, anthracite, granular activated carbon, or crystobalite with a particle size of

approximately 0.5 mm are usually employed.

Modification of Anaerobic Process

• Novel bioreactors for methane fermentation such as the UASB, UAFP, and AFBR experience inherent problems when operated at high COD loads �overall growth rate of acidogenicbacteria proceeds faster (10-fold) than that of methanogenic bacteria. that of methanogenic bacteria.

• Inhibitory products such as volatile fatty acids and H2 accumulate in the reactor, slowing down the entire process.

• In order to overcome this, two-phase processes consisting of acidogenic and methanogenic fermentation's have been investigated (16).

• The influent is pumped into the reactor via a

distribution system, where influent and

recycled sludge/effluent are well mixed.

• The first reactor compartment contains an

expanded granular sludge bed, where most

of the COD is converted to biogas.

• The biogas produced in this compartment is

collected by the lower level separator and is

used to generate a gas lift by which water

and sludge are carried upward via the "riser"

pipe to the gas/liquid separator located on

top of the reactor. Here the biogas is

separated from the water/sludge mixture

and leaves the system.

IC Reactor

• Wastewater with low TSS and FOG can be

processed through the reactor in as little

as a few hours, depending on the strength

of the waste.

• OLR :15 to 35 kg COD/m3/d.

• effective for treating wastewaters from

the beverage, brewery and paper

industries.

and leaves the system.

• The water/sludge mixture is directed

downwards to the bottom of the reactor via

the concentric "downer" pipe, resulting in

the internal circulation flow.

• The effluent from the first compartment is

post-treated in the second, low-loaded

compartment, where any remaining

biodegradable COD is removed.

• The biogas produced in the upper

compartment is collected in the top 3-phase

separator, while the final effluent leaves the

reactor via overflow weirs.

Anaerobic Hybrid Reactor• OLR 5- 15 kg COD/m3d.

• This process is used primarily for soluble

organics removal and has similar constraints

in terms of influent FOG and TSS

concentrations.

• The hybrid reactor has been particularly

suitable for wastewaters where the

development of granular sludge has proven to

be difficult, such as in some chemical be difficult, such as in some chemical

industries. The attached growth on the media

in the upper portion of the reactor together

with the formation of a granular or flocculent

sludge bed in the lower section helps

concentrate biomass in the system, thus

promoting better process stability and higher

performance.

• The cross-flow media also serves as an

effective gas-liquid-solids separator, further

enhancing the biomass retention abilities of

the process.

The hybrid reactor is a combination of

suspended- and fixed-film growth processes.

Typically, the upper 50 to 70 percent of the

reactor is filled with cross-flow plastic media

that serves as the fixed-film zone (or anaerobic

filter section). The lower 30 to 50 percent is the

suspended-growth zone (or UASB section). A

schematic diagram of the ADI-Hybrid reactor is

provided as an example of such technology that

is available commercially

Parameter Pengontrolan Proses

1. pH dan alkalinitas

2. Kebutuhan nutrien

3. temperatur

pH dan alkalinitas

• Bakteri metanogen sensitif terhadapperubahan pH (6,6 -7,6)

• Proses anaerob berlangsung padakisaran pH 6-8

• Kontrol pH � sistem kimia : kesetimbangan karbon dioksida �

penyangga pH

• Alkalinitas bikarbonat ≈ total • Alkalinitas bikarbonat ≈ total alkalinitas ( jumlah total asam yang dapat dinetralkan oleh basa yang tambahkan ke dalam sistem)

• Alkalinitas bikarbonat 2500-5000 mg/l

• Akalinitas:– Alami : OH-; CO3

2-; HCO3-; (Ca2+, Mg2+,

Na+, NH4+)

– Artifisial : kapur & NaOH

Akumulasi VA indikator ketidakseimbangan

sistem dalam reaktor, (asetat 13 mM dan

propionat /asetat = 1,4)

Kebutuhan Nutrien dan Temperatur

• Proses biologi memerlukan nutrien anorganik

• Nutrien anorganik : N dan P

• Perbandingan minimum C : N : P = 100 : 6 : 1

(Jennet dan Dennis, 1979)(Jennet dan Dennis, 1979)

• Optimal temperatur untuk metanogenesis 28-

35oC

Kondisi Reaktor

• Bebas dari Dissolved O2

• Bebas dari H2S dan logam berat � konsentrasiinhibitor

• pH 6,6-7,6• pH 6,6-7,6

• Alkalinitas cukup untuk mencegah pH turun < 6,2 (alkalinitas 1000-5000 mg/l)

• VFA < 250 mg/l

• Cukup N&P

• Suhu mesofilik (30-38C) ; termofilik (49-57C)

Konfigurasi Umum