Beginning in the 1970s and extending into the 1980s, a new class of aerobic attached growth processes became established alternatives for biological wastewater treatment. These are up flow and down flow packed-bed reactors and fluidized-bed reactors that do not use secondary clarification. Their unique advantage is the small footprint with an area requirement that is a fraction (one-fifth to one-third) of that needed for activated-sludge treatment. Though they are more compact, their capital costs are generally higher than that for activated-sludge treatment. In addition to BOD removal, submerged attached growth processes have also been used for tertiary nitrification and de nitrification following suspended or attached growth nitrification.
Down flow and up flow packed-bed reactors, feudalized-bed reactors, and submerged RBC can be used for post anoxic de nitrification. Trickling filters and up flow packed bed reactors are also used for pre anoxic de nitrification. ACSION has developed this unique design in such a way that of simple to operate and stability in the treated water quality have attracted to this design. Our technical expertise is still working in the R&D to upgrade this technique to the most modern design. Keeping in view the fruit of the advantage can be enjoyed by the valued customer.
The Rational For UASB Treatment ( Upflow anaerobic-sludge blanket) The rationale for an interest in the use of anaerobic treatment processes can be explained by considering the advantage and disadvantage of these processes. The principal advantage and disadvantages of anaerobic treatment are listed in table 1.1 and are discussed below.
Advantages of anaerobic treatment processes The prime advantages of ATP are energy considerations; lower biomass yield, fewer nutrients required, and higher volumetric loading are examined further in the following discussion.
Advantages- Less energy required
- Less biological sludge production
- Fewer nutrients required
- Methane production, a potential energy source
- Smaller reactor volume required
- Elimination of off-gas air pollution
- Rapid response to substrate addition after long
- Periods without feeding
Disadvantages- Longer start-up time to develop necessary biomass inventory
- May require alkalinity addition
- May require further treatment with an aerobic treatment process to meet discharge requirements
- Biological nitrogen and phosphorus removal is not possible
- Much more sensitive to the adverse effect of lower temperatures on reaction rates
- May be more susceptible to upsets due to toxic substances
- Potential for production of odors and corrosive
Energy Consideration Anaerobic processes may be net energy users, as is the case for aerobic processes. An energy balance comparison for a high-strength wastewater at 20C is presented in table 1.2. for the conditions given in table 1.2, the aerobic process requires 1.9 x 106 kj/d. on the other hand, the anaerobic process produces a total of 12.5 x 106kj/d. of the total energy produced anaerobically, about 2.1 x 106 kj/d is required to raise the temperature of the wastewater from 20 to 30C, the low end of the mesophilic temperature range, a more desirable temperature for anaerobic treatment. Thus the potential net energy production that can be achieved with anaerobic treatment is on the order of 10.4 x 106 kj/d or about 5 times the energy required for anaerobic treatment.
The wastewater strength is important for comparing energy balances for aerobic and anaerobic processes where the wastewater temperature must be increased. with the same assumptions used to generate the energy balance presented in table 1.2, both the aerobic and anaerobic processes would require the same amount of energy input if the wastewater biodegradable cod concentration is 1270 mg/l. at lower cod concentrations, the aerobic process requires less energy. However, hear recovery from the anaerobic effluent stream can modify these values. Further, the lower biomass yield discussed below is still a major advantage offered by anaerobic treatment.
Lower Biomass Yield Because the energetic of anaerobic processes result in lower biomass production by a factor of about 6 to 8 times produced from aerobic processes are discussed. The fact less sludge is produced in anaerobic treatment is a significant advantage over aerobic treatment.
Fewer Nutrients Required Many industrial wastewaters lack sufficient nutrients to support aerobic growth. The cost for nutrient addition is much less for anaerobic processes because less biomass is produced.
Higher Volumetric loadings. Anaerobic processes generally have higher volumetric organic loads than aerobic processes, so smaller reactor volumes and less space may be required for treatment. Organic loading rates of 3.2 to 32 kg cod/m3.d may be used for anaerobic processes, compared to 0.5 to 3.2 kg cod/m3.d for aerobic processes (speece, 1996).
Disadvantages of Anaerobic Treatment process Potential disadvantages also exist for anaerobic processes as reported in table 1.1. Operational considerations, the need for alkalinity addition, and the need for further treatment are highlighted further in the following discussion.
Operational Considerations The major concerns with anaerobic processes are their longer start-up time (months for anaerobic versus days for aerobic processes), their sensitivity to possible toxic compounds, operational stability, the potential for odor production, and corrosiveness of the digester gas. However, with proper wastewater characterization and process design these problems can be avoided and/or managed.
Need For Alkalinity The most significant negative factor that can affect the economics of anaerobic versus aerobic treatment is the possible need to add alkalinity. Alkalinity concentrations of 2000 to 3000 mg/l as caco3 may be needed in anaerobic processes to maintain an accept pH with the high gas phase co2 concentration. If this amount of alkalinity is not available in the influent wastewater or cannot be produced by the degradation of proteins and amino acid, a significant cost may be incurred to purchase alkalinity, which can affect the overall economics of the process.
Need For Further Treatment Anaerobic processes can also be followed by aerobic processes for effluent polishing to utilize the benefits of both processes. Series reactors of anaerobic aerobic processes have been shown feasible for treating municipal wastewaters in warmer climates resulting in lower energy requirements and less sludge production.
Delhi, India
Verified
Add Review
