Abstract
The excess sludge problem from a wastewater treatment plant is a great concerned due to the high cost of sludge management accounting for about 20% to 50% of the total operating cost. Therefore, sludge reduction is critical. Currently, aerobic and/or anaerobic sludge digestions are widely used in the industries for treating the excess sludge. The objective of this research was to study the effects of aeration rate and temperature on the excess sludge reduction by using the aerobic-anaerobic digestion system in the laboratory. The aeration rates of 1.0, 0.5, and 0.1 volume air per volume slurry per minute (vvm) at the room temperature and the thermophilic temperature (55 ± 2°C) were investigated. The results showed that the highest removal efficiency of aerobic sludge digestion was obtained at the thermophilic temperature and aeration rate of 1.0 vvm. The removal efficiency of organic matter in terms of COD, total solids (TS) and volatile solids (VS) were 34.76%, 33.01% and 43.45%, respectively. Consequently, the highest specific growth rate of microorganisms was 0.39 per hour and the substrate removal rate was 0.55 milligram CODremoved per milligram VSS per hour. Furthermore, slowly biodegradable organic matter was hydrolyzed to readily biodegradable organic matter and inert soluble organic matter. When the sludge effluent from aerobic sludge digestion was feed to the anaerobic sludge digestion, the removal efficiency of organic matter in terms of COD, TS and VS were increased by 25%, 17% and 28%, respectively. Moreover, the obtained methane production rate in the anaerobic sludge digestion was approximate 0.234 m3/kg COD removed.
Highlights
The activated sludge process is the most widely used biological process for domestic wastewater treatment
1.0 vvm 0.5 vvm 0.1 vmm Temperature and aeration rate are the factors affecting the removal of organic matter in the aerobic digestion process because, at high temperature, the dissolve oxygen was limited and the amount used in the decomposition of organic matter not enough
The results showed that the highest removal efficiency of the aerobic sludge digestion was obtained at the thermophilic temperature and aeration rate of 1.0 vvm
Summary
The activated sludge process is the most widely used biological process for domestic wastewater treatment. Organic pollutants are mineralized into carbon dioxide and water with the generation of an excess bacterial biomass commonly known as a waste activated sludge. Sludge stabilization is employed to deduct germs and prevent sludge decomposition. The aerobic digestion process is similar to the method of the activated sludge (AS), which aims at eliminating organic dust or volatile solid. Does the aerobic digestion stabilize sludge, but it reduces the quantity of excess sludge from the process [3,4,5]. The dewatering process can be achieved more and the sludge decomposition is prevented [6]
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