Benyi Xiao

Enhancing simultaneous electricity production and reduction of sewage sludge in two-chamber MFC by aerobic sludge digestion and sludge pretreatments.

Batch tests were conducted to enhancing simultaneous electricity production and reduction of sewage sludge in two-chamber MFC by aerobic sludge digestion in cathode chamber and sludge pretreatments (sterilization and base pretreatment) prior to sludge addition to anode chamber, respectively. During the stable stage, The voltage outputs and power densities of MFC increased from 0.28-0.31 V to 17.3-21.2 mW/m(2) to 0.41-0.43 V and 36.8-40.1 mW/m(2), respectively, when aerobic sludge digestion occurred in the cathode chamber. When the sludge added to the anode chamber was sterilized or base pretreated, the voltage outputs and power densities of MFC increased from 0.30-0.32 V and 19.9-22.6 mW/m(2) (raw sludge) to 0.34-0.36 V and 25.5-28.6 mW/m(2) (sterilized sludge), 0.41-0.43 V and 37.1-40.8 mW/m(2) (base pretreated sludge), respectively. At the end of the test, the total suspended solids (TSS) and volatile suspended solids (VSS) reduction of sludge in the anode chambers increased from 33.9% and 36.8% to 34.5% and 38.7% with aerobic sludge digestion in the cathode chamber, respectively; while, those (TSS and VSS reduction) with sludge pretreatments prior to the sludge addition to the anode chambers increased from 25.1% and 22.8% (raw sludge) to 32.8% and 34.6% (sterilized sludge), and 25.5% and 26.7% (base pretreated sludge), respectively. The experimental results illuminated both aerobic sludge digestion in the cathode chamber and sludge pretreatments (sterilization and base pretreatment) prior to sludge addition to the anode chamber could enhance simultaneous electricity production from sludge and sludge reduction.

Biological hydrogen production from sterilized sewage sludge by anaerobic self-fermentation

Due to richness in proteins and carbohydrates, the sewage sludge produced from the wastewater treatment processes is becoming a potential substrate for biological hydrogen production. In this study, sterilized sludge was employed to produce hydrogen by batch anaerobic self-fermentation without any extra-feeds and extra-seeds. Sterilization can screen hydrogen-producing microorganisms from sludge microflora and release organic materials from microbial cells of sludge. Experimental results suggested that sterilization could accelerate and increase the hydrogen production of sewage sludge in the anaerobic self-fermentation, and the biogas did not contain methane. The hydrogen yield was increased from 0.35 mL H(2)/g VS (raw sludge) to 16.26 m LH(2)/g VS (sterilized sludge). Although sterilization could fully inhibit the activity of methanogens in the sludge, the hydrogen consumption still occurred in the anaerobic self-fermentation of sterilized sludge due to the existence of other hydrogen-consuming actions. The decrease of pH in the anaerobic self-fermentation of sterilized sludge was very lower (from 6.81 to 6.56) because NH(4)(+) produced by degradation of proteins could neutralize organic acids produced in the process. The soluble chemical oxygen demand (SCOD) increase of sterilized sludge was higher than that of raw sludge. Volatile fatty acids (VFA) were the important by-products and acetate was the major composition. The hydrogen fermentation of carbohydrates was the major source of hydrogen production.

Evaluation of the microbial cell structure damages in alkaline pretreatment of waste activated sludge

This study investigated the damages of microbial cell structures, as well as the relationships between these damages and the release of cellular organic matter in the pretreatment of waste activated sludge (WAS) by using alkaline pretreatment as model. In the alkaline pretreatment of WAS, the most damage of bound extracellular polymeric substances (EPS), cell walls, cell membranes, and cell nuclei occurred at pH 11.5-12.0 (46.2%), pH 11.0-11.5 (27.3%), pH 9.0-10.0 (34.2%), and pH 11.5-12.0 (44.4%), respectively. The damage percentages of these cell structures in the pH stabilization stage were low because most of the damages occurred when the pH increased. The structural integrities of sludge microorganisms were all damaged in the pH increase stage. The damages of EPS, cell walls, and cell membranes were significantly correlated with the release of cellular organic matter, and these damages were necessary to release the cellular matter in WAS.

Evaluation of electricity production from alkaline pretreated sludge using two-chamber microbial fuel cell

Electricity production from alkaline pretreated sludge was evaluated using a two-chamber microbial fuel cell (MFC). The electricity production was found to be stable over a long period of time (approximately 17 d) with voltage outputs and power densities of 0.47-0.52 V and 46.80-55.88 mW/m(2), respectively. The anode resistance was the main internal resistance (73.2%) of MFC in the stable stage. Most soluble organic matters (proteins and carbohydrates) in the anode chamber were first degraded and converted into volatile fatty acids (0-15 d), which were then degraded and converted into electricity and methane (15-29 d). The insoluble organics were solubilized thereby decreasing the sludge concentration and reducing the sludge mass. Methane was produced in the anode chamber owing to the growth of methanogens, which did not obviously affect the electricity production. The change in humic-like substances displayed a positive correlation with the electricity production of the MFC. Microbial analysis showed that methanogens and electricity-producing bacteria co-existed mostly on the surface as well as inside the anode. Decreasing the anode resistance and increasing the anode utilization could enhance the electricity production.

Evaluation of the damage of cell wall and cell membrane for various extracellular polymeric substance extractions of activated sludge

Extracellular polymeric substances (EPS) are susceptible to contamination by intracellular substances released during the extraction of EPS owing to the damage caused to microbial cell structures. The damage to cell walls and cell membranes in nine EPS extraction processes of activated sludge was evaluated in this study. The extraction of EPS (including proteins, carbohydrates and DNA) was the highest using the NaOH extraction method and the lowest using formaldehyde extraction. All nine EPS extraction methods in this study resulted in cell wall and membrane damage. The damage to cell walls, evaluated by 2-keto-3-deoxyoctonate (KDO) and N-acetylglucosamine content changes in extracted EPS, was the most significant in the NaOH extraction process. Formaldehyde extraction showed a similar extent of damage to cell walls to those detected in the control method (centrifugation), while those in the formaldehyde-NaOH and cation exchange resin extractions were slightly higher than those detected in the control. N-acetylglucosamine was more suitable than KDO for the evaluation of cell wall damage in the EPS extraction of activated sludge. The damage to cell membranes was characterized by two fluorochromes (propidium iodide and FITC Annexin V) with flow cytometry (FCM) measurement. The highest proportion of membrane-damaged cells was detected in NaOH extraction (26.54% of total cells) while membrane-damaged cells comprised 8.19% of total cells in the control.

Consequences of sludge composition on combustion performance derived from thermogravimetry analysis

Wastewater treatment plants produce millions of tons of sewage sludge. Sewage sludge is recognized as a promising feedstock for power generation via combustion and can be used for energy crisis adaption. We aimed to investigate the quantitative effects of various sludge characteristics on the overall sludge combustion process performance. Different types of sewage sludge were derived from numerous wastewater treatment plants in Beijing for further thermogravimetric analysis. Thermogravimetric-differential thermogravimetric curves were used to compare the performance of the studied samples. Proximate analytical data, organic compositions, elementary composition, and calorific value of the samples were determined. The relationship between combustion performance and sludge composition was also investigated. Results showed that the performance of sludge combustion was significantly affected by the concentration of protein, which is the main component of volatiles. Carbohydrates and lipids were not correlated with combustion performance, unlike protein. Overall, combustion performance varied with different sludge organic composition. The combustion rate of carbohydrates was higher than those of protein and lipid, and carbohydrate weight loss mainly occurred during the second stage (175-300°C). Carbohydrates have a substantial effect on the rate of system combustion during the second stage considering the specific combustion feature. Additionally, the combustion performance of digested sewage sludge is more negative than the others.

Effects of sludge thermal-alkaline pretreatment on cationic red X-GRL adsorption onto pyrolysis biochar of sewage sludge.

Thermal-alkaline pretreatment has traditionally been used to enhance anaerobic sludge digestion. In this study, after removing the supernatant, which could be used in anaerobic digestion, the Residual Solids of Thermal-Alkaline pretreated sewage Sludge (RSTAS) were used to prepare biochar via pyrolysis, which could then adsorb Cationic Red X-GRL(X-GRL). The experimental results showed that the RSTAS-biochar had a higher BET surface area and total pore volume than the biochar prepared from raw sludge (RS) (43.5% and 33.3%, respectively). The pretreatment enhanced the X-GRL adsorption capacity of the biochar by 1.5-49.2% at dosages between 12.5-100.0g/g, and the highest adsorption capacity increased from 39.1mg/g to 47.6mg/g. The biochar from RSTAS had a wider application pH range for X-GRL adsorption. The kinetics and isotherms for X-GRL adsorption onto the two biochars were well fitted to the pseudo-second-order and Langmuir isotherm models, respectively, which suggested that thermal-alkaline pretreatment had little effect on the adsorption mechanisms of X-GRL onto biochar.

Temperature-phased anaerobic digestion of food waste: A comparison with single-stage digestions based on performance and energy balance.

The temperature-phased anaerobic digestion (TPAD) of food waste was studied for the purpose of comparing with single-stage mesophilic and thermophilic anaerobic digestion. The biogas and methane yields in the TPAD during the steady period were 0.759 ± 0.115 L/g added VS and 0.454 ± 0.201 L/g added VS, which were lower than those in the two single-stage anaerobic digestion. The improper sludge retention time may be the reason for the lower biogas and methane production in TPAD. The removal of volatile solids in the TPAD was 78.55 ± 4.59% and the lowest among the three anaerobic digestion processes. The reaction ratios of the four anaerobic digestion steps in the TPAD were all lower than those in the two single-stage anaerobic digestion. The energy conversion efficiency of the degraded substrate in the TPAD was similar with those in single-stage mesophilic and thermophilic anaerobic digestion systems.

Electricity production and sludge reduction by integrating microbial fuel cells in anoxic-oxic process

To produce energy and reduce sludge production from the treatment of municipal wastewater, four identical microbial fuel cells (MFCs) were constructed in an anoxic-oxic (A/O) process (MFCs-A/O system). Experimental results indicated that this system enhance the removals of chemical oxygen demand (COD) and total nitrogen (TN). The electricity produced by each MFC were ranged from 0.371 to 0.477V (voltage) and from 138 to 227mW/m3 (power density) at the stable stage, when the external resistance was fixed at 1000Ω. The coulombic efficiency of the MFCs-A/O system ranged from 0.31% to 1.68% (mean=0.72%) at the stable stage, respectively. The removals of COD and TN in the MFCs-A/O system were slightly higher than those in the control system. Compared with the control system, the MFCs-A/O system can reduce waste activated sludge production and sludge yield by 24.0% and 24.2%, respectively. The experimental results indicated that the MFC constructed in A/O system improves wastewater treatment and the MFCs-A/O system can produce electricity while reducing sludge production and increasing wastewater treatment efficiency.

Effects of wastewater treatment processes on the sludge reduction system with 2,4-dichlorophenol: Sequencing batch reactor and anaerobic-anoxic-oxic process

The effects of two wastewater treatment processes (sequencing batch reactor, SBR; and anaerobic-anoxic-oxic, A2O) on sludge reduction with metabolic uncoupler 2,4-dichlorophenol (DCP) were studied in laboratory. The experimental results showed that the reduction of cumulative excess sludge in SBR and A2O was 43.7% and 44.2%, respectively, during the stable stage of the test. The two processes had similar average sludge yield and sludge yield reduction, i.e., 0.306 and 0.305mg of SS/mg chemical oxygen demand (COD), and 16.9% and 17.8%, respectively. The effect of DCP on the wastewater treatment efficiencies (namely, removal of COD, total nitrogen, NH4+-N, and total phosphorus) of the two processes were also similar. SBR was more likely to slightly retard the increase of activated sludge SVI with lesser increase in extracellular polymeric substances and protein/polysaccharide ratio. Although DCP did not dramatically affect the microbial communities of sludge, SBR was more favorable for increasing the activated sludge SOUR and maintaining the primary microorganisms of sludge than A2O.