Yawei Wang

Optimization and microbial community analysis of anaerobic co-digestion of food waste and sewage sludge based on microwave pretreatment

The effects of microwave pretreatment (MW) on co-digestion of food waste (FW) and sewage sludge (SS) have never been investigated. In this study, a series of mesophilic biochemical methane potential (BMP) tests were conducted to determine the optimized ratio of FW and SS based on MW, and the evolution of bacterial and archaeal community was investigated through high-throughput sequencing method. Results showed that the optimized ratio was 3:2 for co-digestion of FW and SS based on MW, and the methane production was 316.24 and 338.44mLCH4/gVSadded for MW-FW and MW-SS, respectively. The MW-SS was superior for methane production compared to MW-FW, in which accumulation of propionic acid led to the inhibition of methanogenesis. Proteiniborus and Parabacteroides were responsible for proteins and polysaccharides degradation for all, respectively, while Bacteroides only dominated in co-digestion. Methanosphaera dominated in MW-FW at the active methane production phase, while it was Methanosarcina in MW-SS and mono-SS.

Effect of H2O2 dosing strategy on sludge pretreatment by microwave-H2O2 advanced oxidation process

Considering characteristics of breaking down H(2)O(2) into water and molecular oxygen by catalase in waste activated sludge (WAS), the effect of H(2)O(2) dosing strategy on sludge pretreatment by the advanced oxidation process (AOP) of microwave-H(2)O(2) was investigated by batch experiments for optimizing H(2)O(2) dosage. Results showed that the catalase in sludge was active at the low temperature range between 15 degrees C and 45 degrees C, and gradually lost activity from 60 degrees C to 80 degrees C. Therefore, the H(2)O(2) was dosed at 80 degrees C, to which the waste activated sludge was first heated by the microwave (MW), and then the sludge dosed with H(2)O(2) was continuously heated till 100 degrees C by the microwave. Results at different H(2)O(2) dosages showed that the higher the H(2)O(2) dosing ratio was, the more the SCOD and total organic carbon (TOC) were released into the supernatant, and the optimum range of H(2)O(2)/TCOD ratio should be between 0.1 and 1.0. The percentages of consumed H(2)O(2) in the AOP of microwave and H(2)O(2) treating the WAS were 25.38%, 22.53%, 14.82%, 13.61% and 19.63% at different H(2)O(2)/TCOD dosing ratios of 0.1, 0.5, 1, 2, 4, respectively. Along with the increasing H(2)O(2)/TCOD ratio, the contents of TCOD on particles, soluble substances and mineralization increased and the TCOD distribution on solids decreased.

Sludge reduction potential of the activated sludge process by integrating an oligochaete reactor

An oligochaete reactor linked to an integrated oxidation ditch with vertical cycle (IODVC) was used to investigate the sludge reduction potential induced by worms. The presence of Tubificidae was observed in the worm reactor throughout the operational period after its inoculation, and Tubificidae was occasionally found in the IODVC. Free-swimming worms, Aeolosoma hemprichi, Nais elinguis, and Aulophorus furcatus, were found in both the IODVC and the worm reactor, but A. hemprichi was dominant. A. hemprichi reached its maximum, 322 and 339 Aeolosoma/mL mixed liquor on day 49 in the worm reactor and the IODVC, respectively. The presence of oligochaetes or the integration of worm reactor with the IODVC had little effect on sludge yield, but the worm growth was helpful for improving sludge settling characteristics. The average sludge yield and sludge volume index (SVI) in the IODVC were 0.33 kgSS/kgCOD(removed) and 78 mL/g, respectively. The worm presence had little impact on effluent quality of the IODVC, but it caused phosphorus release into the effluent. The average COD, NH(4)(+)-N, and SS concentrations in the effluent of the IODVC were 49.06, 12.82, and 58.25 mg/L, respectively. No total nitrogen (TN) release into the effluent of the IODVC occurred.

Microwave-acid pretreatment: A potential process for enhancing sludge dewaterability.

Activated sludge is hard to be dewatered due to the highly water bounded in sludge flocs. This study investigated the hybrid treatment of microwave irradiation and acidification on sludge dewaterability as well as its mechanism. Results showed that the combined microwave-acid treatment (Txa0=xa0100xa0°C, initial pHxa0=xa02.5) was effective for improving sludge dewaterability, e.g. capillary suction time (CST) decreased from 37.7xa0s to 9.2xa0s, bound water content decreased from 1.96xa0±xa00.19xa0g/g Dry Sludge (DS) to 0.88xa0±xa00.24xa0g/g DS. The treated sludge showed more fluidity and less thixotropy. Both MW heating temperature and pH played important roles in improving sludge dewaterability. Higher temperature was beneficial for sludge disintegration, but the released polymers resulted in highly negative zeta potential and deteriorated sludge dewaterability. The acidification was capable of reducing the negative zeta potential, increasing flocs size and finally improving sludge dewaterability. According to the analysis of molecule weight distribution and 3D-EEM, the fractions of polymers especially protein-like substances at molecule weight of 10(4)-10(5)xa0Da were the key organics related to sludge dewaterability, but not the humic acid-like and fulvic acid-like substances.

Pilot-scale study of sludge pretreatment by microwave and sludge reduction based on lysis-cryptic growth

To evaluate the performance of microwave (MW)-chemical hybrid sludge treatment system, a pilot scale MW disintegration unit (treatment capacity of 500L/d) was constructed. The results showed that organic matter, nitrogen, and phosphorus were effectively released from the MW-pretreated sludge. The values of COD released were 15.91%, 15.07%, 13.83%, 19.35%, and 15.07% for the MW, MW-acid, MW-alkali, MW-H2O2, and MW-H2O2-alkali treatment processes, respectively. Additionally, for a wastewater treatment system with a capacity of 200m(3)/d, when coupled with a MW sludge pretreatment unit, the sludge production and sludge yield were greatly reduced by 38.60% and to 0.35kg VSS/kg CODconsumed, respectively. The total operating cost of the lysis-cryptic growth system was 13.64% lower than that of the CAS system without a MW unit.

Chemical forms and risk assessment of heavy metals in sludge-biochar produced by microwave-induced low temperature pyrolysis

Biochar, a stable, carbon-rich solid produced during biomass pyrolysis, has been widely used in soil conditioning. A promising option to alleviate the problem of sludge management. In this study, Cr, Ni, Zn, Cd, As, Pb and Cu were studied owing to their relatively high content in the sludge and their potential to cause environmental damage. Sludge-biochars were produced at different temperatures (300xa0°C, 350 °C, 400 °C and 450 °C) by microwave pyrolysis. BCR (European Community Bureau of Reference: a sequential extraction) analysis reveals that speciation distribution varied largely with the different heavy metals. Three risk analysis models were adopted to evaluate the risk of heavy metals: the risk assessment code (RAC), geo-accumulation index (Igeo) and potential ecological risk index (Er). The heavy metals risk in the biochar were lower compared with the sludge except for Pb (sludge: 4.3, biochar: 9.4–15.6) as assessed by RAC analysis. The Er result shows that risk from heavy metals decreased except for Cd (sludge: 63.53, biochar: 153.53–189.38). The Igeo model indicated that all seven heavy metals were present at higher levels in biochar than in the sludge. Although the total metal concentration in biochar increased after pyrolysis, this result indicates that heavy metal risk of microwave pyrolysis sludge-biochar should be considered alongside local soil backgrounds and speciation distributions.

Effects of aeration on matrix temperature by infrared thermal imager and computational fluid dynamics during sludge bio-drying

The effect of aeration on the pile matrix temperature was investigated using thermocouples and Infrared Thermal Imager (IRI) for temperature sensing, and Computational Fluid Dynamics (CFD) for modelling of temperature variation during aeration in a full-scale sludge biodrying plant. With aeration saving of 20%, the improved strategy speeded up biodrying from 21 days to 14 days, while achieving similar drying effect. A persistent thermocouple recorded the one-dimensional (1D) total temperature variation of all aeration strategies. The IRI captured the rapid two-dimensional (2D) pile temperature dropped from 72.5xa0°C to 30.3xa0°C during 6xa0min of aeration, which mechanism suggested as the latent heat of moisture evaporation and sensible heat of air exchange. The CFD three-dimensional (3D) CFD results highlight the importance of latent heat rather than sensible heat. Therefore, the pile temperature drop inferred is ΔTxa0=xa05.38xa0°C theoretically and ΔTxa0=xa05.17xa0±xa04.56xa0°C practically, per unit of MC removed. These findings also emphasize the possibility of a pile temperature valley, due to excessive aeration under unsaturated vapour conditions. Surface temperature monitored by IRI coupled with 3D temperature simulated by CFD rapidly gives a clear matrix temperature evolution, empowering biodrying by more accurate temperature and aeration.

Spatio-temporal distribution of fecal indicators in three rivers of the Haihe River Basin, China

Because of their significant impact on public health, waterborne pathogens, especially bacteria and viruses, are frequently monitored in surface water to assess microbial quality of water bodies. However, more than one billion people worldwide currently lack access to safe drinking water, and a diversity of waterborne outbreaks caused by pathogens is reported in nations at all levels of economic development. Spatio-temporal distribution of conventional pollutants and five pathogenic microorganisms were discussed for the Haihe River Basin. Land use and socio-economic assessments were coupled with comprehensive water quality monitoring. Physical, chemical, and biological parameters were measured at 20 different sites in the watershed for 1xa0year, including pH, temperature, conductivity, dissolved oxygen, turbidity, chemical oxygen demand, ammonia-N, total and fecal coliforms, E. coli, and Enterococcus. The results highlighted the high spatio-temporal variability in pathogen distribution at watershed scale: high concentration of somatic coliphages and fecal indicator bacteria in March and December and their very low concentration in June and September. All pathogens were positively correlated to urban/rural residential/industrial land and negatively correlated to other four land use types. Microbial pollution was greatly correlated with population density, urbanization rate, and percentage of the tertiary industry in the gross domestic product. In the future, river microbial risk control strategy should focus more on the effective management of secondary effluent of wastewater treatment plant and land around rivers.