Effect Of Sludge Pretreatment Research Articles

Enhancing the anaerobic digestion potential of dairy waste activated sludge by two step sono-alkalization pretreatment

High efficiency resource recovery from dairy waste activated sludge (WAS) has been a focus of attention. An investigation into the influence of two step sono-alkalization pretreatment (using different alkaline agents, pH and sonic reaction times) on sludge reduction potential in a semi-continuous anaerobic reactor was performed for the first time in literature. Firstly, effect of sludge pretreatment was evaluated by COD solubilization, suspended solids reduction and biogas production. At optimized condition (4172kJ/kg TS of supplied energy for NaOH – pH 10), COD solubilization, suspended solids reduction and biogas production was 59%, 46% and 80% higher than control. In order to clearly describe the hydrolysis of waste activated sludge during sono-alkalization pretreatment by a two step process, concentrations of ribonucleic acid (RNA) and bound extracellular polymeric substance (EPS) were also measured. Secondly, semi-continuous process performance was studied in a lab-scale semi-continuous anaerobic reactor (5L), with 4L working volume. With three operated SRTs, the SRT of 15 d was found to be most appropriate for economic operation of the reactor. Combining pretreatment with anaerobic digestion led to 58% and 62% of suspended solids and volatile solids reduction, respectively, with an improvement of 83% in biogas production. Thus, two step sono-alkalization pretreatment laid the basis in enhancing the anaerobic digestion potential of dairy WAS.

Influence of the thermochemical sludge pretreatment on the nitrification of A/O reactor with the removal of phosphorus by simultaneous precipitation

In the present study, a laboratory scale anoxic/oxic (A/O) reactor is used for the removal of nutrient and sludge reduction. Phosphorus removal was achieved through simultaneous precipitation, and sludge production was reduced through thermochemical pretreatment. The main objective of the study was to investigate the influence of sludge pretreatment on the nitrification rate. Total phosphorus in the effluent was maintained around 0.5 ∼ 1.0 mg/L by simultaneous precipitation, using coagulant alum at 2.2 mole ratio. Before simultaneous precipitation, the nitrification rate of the A/O reactor was found to be 0.050 g N-NH4+/g MLVSS.d. The thermochemical sludge pretreatment began on the 120th day at pH 11 and 80°C. The initiation of sludge pretreatment brought about a significant reduction of the A/O reactor nitrification rate, which fell to 0.038 g N-NH4+/g MLVSS/day. The effect of sludge pretreatment was reflected in the reduction of the nitrogen removal efficiency from 85 to 74%. Recycling of the thermochemically pretreated sludge accounted for 57% sludge reduction, which had an adverse influence on the nitrification rate of the system.

Effects of sludge pretreatment on sludge reduction in a lab-scale anaerobic/anoxic/oxic system treating domestic wastewater

Excess sludge disposal is one of the serious challenges in biological wastewater treatment. Reduction of sludge production would be an ideal way to solve sludge- associated problems rather than the post-treatment of the sludge produced. In this study, a new wastewater treatment process combining anaerobic/anoxic/oxic system with thermochemical sludge pretreatment was tested in a labo- ratory scale experiment. In this study, the effects of the sludge pretreatment on the excess sludge production in anaerobic/anoxic/oxic were investigated. The system was operated in two Runs (1 and 2). In Run 1, the system was operated as a reference and in Run 2, a part of the mixed liquid was pretreated thermochemically and was returned to the bioreactor. The average solubilization efficiency of pretreated sludge was found to be about 35 % during the study period of 220 days. Sludge production rate in Run 2 was less than that in Run 1 by about 52 %. Total phos- phorous was removed by enhanced biological phosphorous removal with the removal efficiency of 83-87 % and 81-83 % for Run 1 and Run 2, respectively. Total nitrogen removal in Run 2 (79-82 %) was slightly higher than that in Run 1 (68-75 %). The mixed liquor suspended solids/ mixed liquor volatile suspended solids ratio was identical after both runs in the range 78-83 %. The effluent water qualities were not significantly affected when operated with thermochemical pretreatment at pH 11 and 60 C for 3 h during 7 months. From the present study it is concluded that thermochemical sludge pretreatment of anaerobic/anoxic/ oxic process plays an important role in reduction of sludge production.

Combined treatment of alkaline and disperser for improving solubilization and anaerobic biodegradability of dairy waste activated sludge

An investigation into the influence of combined alkaline and disperser pretreatment on sludge disintegration was studied. The effects of four variables, alkalines (NaOH, KOH, Ca(OH)2), treatment time (15–180min), pH (8–11) and rpm (4000–24,000) were investigated. The effect of sludge pretreatment was evaluated by COD solubilization, suspended solids reduction and biogas production. The best performances, in terms of COD solubilization, SS reduction and biogas production, were the ones that occurred for specific energy input of 4544kJkg−1 TS for NaOH at pH10, were found to be 24%, 23.3% and 76%, higher than the control, respectively. Not only the increase in biogas production was investigated, excluding protein hydrolysis was also performed successfully by this combined pretreatment even at low specific energy input. Thus, this chemo-mechanical is an effective method for enhancement of biodegradability and it laid the basis to produce higher biogas quantities, to improve clean energy generation from WAS.

Low temperature thermo-chemical pretreatment of dairy waste activated sludge for anaerobic digestion process

An investigation into the influence of low temperature thermo-chemical pretreatment on sludge reduction in a semi-continuous anaerobic reactor was performed. Firstly, effect of sludge pretreatment was evaluated by COD solubilization, suspended solids reduction and biogas production. At optimized condition (60°C with pH 12), COD solubilization, suspended solids, reduction and biogas production was 23%, 22% and 51% higher than the control, respectively. Secondly, semi-continuous process performance was studied in a lab-scale semi-continuous anaerobic reactor (5L), with 4L working volume. With three operated SRTs, the SRT of 15days was found to be most appropriate for economic operation of the reactor. Combining pretreatment with anaerobic digestion led to 80.5%, 117% and 90.4% of TS, SS and VS reduction respectively, with an improvement of 103% in biogas production. Thus, low temperature thermo-chemical can play an important role in reducing sludge production.

Effect of sludge pretreatment on the performance of anaerobic/ anoxic/ oxic membrane bioreactor treating domestic wastewater

In the present study, two bench-scale anaerobic/ anoxic/ oxic submerged membrane bioreactors were used to study the effect of thermochemical sludge disintegration system on the excess sludge production. Among the two membrane bioreactors, one was named experimental membrane bioreactor and another one was named as control membrane bioreactor, where a part of the mixed liquor was treated with thermo chemical and was returned back to membrane bioreactor. Thermo chemical digestion of sludge was carried out at fixed pH (11) and temperature (75 °C) for 24 % chemical oxygen demand solution. The other one was named control membrane bioreactor and was used as control. The reactors were operated at three different mixed liquor suspended solids range starting from 7500 mg/L to 15000 mg/L. Both of membrane bioreactors were operated at a flux of 17 LMH over a period of 240 days. The designed flux was increased stepwise over a period of one week. During the 240 days of reactor operation, both of membrane bioreactors maintained relatively constant transmembrane pressure. The sludge digestion had no impact on chemical oxygen demand removal efficiency of the reactor. The results based on the study indicated that the proposed process configuration has potential to reduce the excess sludge production as well as it didn’t deteriorate the treated water quality.

EVALUATION OF A MEMBRANE BIOREACTOR SYSTEM COUPLED WITH SLUDGE PRETREATMENT FOR AEROBIC SLUDGE DIGESTION

The effects of ozone and alkaline pretreatment of sewage sludge on the performances of membrane-coupled aerobic sludge digestion were investigated. In particular, the effects of sludge pretreatment on the solubilization, sludge biodegradation and the stability of membrane filtration were evaluated. Three sets of reactors were operated under different conditions of sludge treatment; 1) ozone treatment at 0.1 g O3 g-1 suspended solids(SS) of the influent sludge, 2) alkaline treatment at pH 11.4-12.0, 3) no treatment. Without sludge pretreatment, 27% of suspended solids (SS) reduction was obtained at the hydraulic retention time(HRT) of 5 days. With ozone and alkaline treatment, the average SS reduction increased to 83 and 76%, respectively, at the same HRT. Membrane fouling occurred earliest with the non-treated sludge, followed by the alkali-treated sludge. With ozonated sludge, stable membrane filtration for more than 150 days was possible without chemical cleaning of the membrane. The dynamic viscosity of the mixed liquor in the reactor fed with ozonated sludge was relatively low, indicating the role of ozone treatment in controlling membrane fouling. In conclusion, sludge pretreatment followed by aerobic sludge digestion in a membrane-coupled bioreactor can achieve a very high rate of sludge reduction at a relatively short HRT.