ANAEROBIC TREATMENT PROCESS

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. Hidrolisis2. Asidegenesis3. 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+CO2CH4+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).

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 deterioration; and

• Can handle organic shock loads effectively.

Disadvantages

• Anaerobic treatment cannot achieve surface water discharge quality without 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 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.

• 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

Up flow velocity : 0.6 – 0.9 m/h

Granules range in size from 0.5-2.5 mm,

• Influent flow is typically equalized,neutralized and partially acidified in aseparate tank ahead of the reactor.

• The influent flow is often mixed witheffluent recycle and then distributed intothe lower part of the reactor below thesludge bed.

• The upper portion of the reactor typicallyhas a gas-liquid-solids separator (GLSS)that removes biogas and clarifies theeffluent.

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.

• 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 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 distribusihomogen “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 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.

• 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).

• 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.

• 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.

• 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.

IC Reactor

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 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 dioksidapenyangga pH

• 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)

• Optimal temperatur untuk metanogenesis 28-35oC

Kondisi Reaktor

• Bebas dari Dissolved O2

• Bebas dari H2S dan logam berat konsentrasiinhibitor

• 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