Yuansong Wei

MINIMIZATION OF EXCESS SLUDGE PRODUCTION FOR BIOLOGICAL WASTEWATER TREATMENT

Excess sludge treatment and disposal currently represents a rising challenge for wastewater treatment plants (WWTPs) due to economic, environmental and regulation factors. There is therefore considerable impetus to explore and develop strategies and technologies for reducing excess sludge production in biological wastewater treatment processes. This paper reviews current strategies for reducing sludge production based on these mechanisms: lysis-cryptic growth, uncoupling metabolism, maintenance metabolism, and predation on bacteria. The strategies for sludge reduction should be evaluated and chosen for practical application using costs analysis and assessment of environmental impact. High costs still limit technologies of sludge ozonation-cryptic growth and membrane bioreactor from spreading application in full-scale WWTPs. Bioacclimation and harmful to environment are major bottlenecks for chemical uncoupler in practical application. Sludge reduction induced by oligochaetes may present a cost-effective way for WWTPs if unstable worm growth is solved. Employing any strategy for reducing sludge production may have an impact on microbial community in biological wastewater treatment processes. This impact may influence the sludge characteristics and the quality of effluent.

The behavior of tetracyclines and their degradation products during swine manure composting

The purposes of this study were to investigate the behavior of three tetracyclines including chlortetracycline (CTC), oxytetracycline (OTC) and tetracycline (TC) and their degradation products in a pilot scale swine manure composting, and also to study the degradation kinetics of CTC, OTC and TC. During the pilot scale composting, CTC, OTC and TC were degraded by 74%, 92% and 70%, respectively. Several degradation products were found like 4-epitetracycline (ETC), 4-epioxytetracycline (EOTC), 4-epichlortetracycline (ECTC), demeclocycline (DMCTC) and anhydrotetracycline (ATC). Both the simple and the adjusted first-order kinetic models successfully fit the degradation process of CTC, OTC and TC during the composting, but the adjusted first-order kinetic model fit much better with the calculated half-lives of 8.2, 1.1 and 10.0 days, respectively.

Composting and compost application in China

The current situation of municipal solid waste (MSW) and sewage sludge production (in terms of volume as well as composition) in China is introduced. Composting and compost application in China are reviewed. In China, the production of municipal solid waste and sewage sludge is changing rapidly along with economic development. Composting is mainly applied for treating MSW, about 20% of the total amount of MSW being disposed. MSW composting is mainly co-composted with night soil or sewage sludge. Compost is used in agriculture, forestry and horticulture. Compost application is the key factor influencing the composting development in China. To promote composting and compost application in China, a state-wide survey on the production, composition and physical and chemical properties of MSW and sewage sludge should be carried out. More effort should be made to develop low cost and high efficient composting technologies according to Chinas conditions. The environmental impact of compost application should also be given more attention.

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.

Water reuse: >90% water yield in MBR/RO through concentrate recycling and CO2 addition as scaling control.

Over 1.5 years continuous piloting of a municipal wastewater plant upgraded with a double membrane system (ca. 0.6 m(3) d(-1) of product water produced) have demonstrated the feasibility of achieving high water quality with a water yield of 90% by combining a membrane bioreactor (MBR) with a submerged ultrafiltration membrane followed by a reverse osmosis membrane (RO). The novelty of the proposed treatment scheme consists of the appropriate conditioning of MBR effluent prior to the RO and in recycling the RO concentrates back to the biological unit. All the 15 pharmaceuticals measured in the influent municipal sewage were retained below 100 ng L(-1), a proposed quality parameter, and mostly below detection limits of 10 ng L(-1). The mass balance of the micropollutants shows that these are either degraded or discharged with the excess concentrate, while only minor quantities were found in the excess sludge. The micropollutant load in the concentrate can be significantly reduced by ozonation. A low treated water salinity (<10 mM inorganic salts; 280 ± 70 μS cm(-1)) also confirms that the resulting product has a high water quality. Solids precipitation and inorganic scaling are effectively mitigated by lowering the pH in the RO feed water with CO(2) conditioning, while the concentrate from the RO is recycled to the biological unit where CO(2) is stripped by aeration. This causes precipitation to occur in the bioreactor bulk, where it is much less of a process issue. SiO(2) is the sole exception. Equilibrium modeling of precipitation reactions confirms the effectiveness of this scaling-mitigation approach for CaCO(3) precipitation, calcium phosphate and sulfate minerals.

Sludge reduction with Tubificidae and the impact on the performance of the wastewater treatment process.

To reduce excess sludge, a Tubificidae reactor was combined with an integrated oxidation ditch with vertical circle (IODVC), and a new integrated system was developed for wastewater treatment. A pilot-scale of this integrated system was tested to investigate the sludge reduction with Tubificidae and the impact on effluent quality and sludge production. The dominant worm was Branchnria Sowerbyi in the Tubificidae reactor after inoculation of Branchnria Sowerbyi and Limnodrilns sp., and the maximal volume density of wet Tubificidae in vessels of the Tubificidae reactor was 17600 g/m3. Two operational modes, treating the excess sludge (first mode) and the returned sludge (second mode) of IODVC by the Tubificidae reactor, were used in this experiment. The results showed that the excess sludge reduction rate was 46.4% in the first mode, and the average sludge yield of the integrated system was 6.19 x 10(-5) kg SS/kg COD in the second mode. Though the sludge returned to IODVC via the Tubificidae reactor, it had little impact on the effluent quality and the sludge characteristics of the IODVC. No new type of recalcitrant substance in the supernatant was discharged into the environment when the sludge was treated by Tubificidae. The experimental results also indicated that no significant changes occurred on the viscosity, specific resistance, and the floc size distribution of the sludge.

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.

Distribution of antibiotic resistance genes (ARGs) in anaerobic digestion and land application of swine wastewater

Swine farm and the adjacent farmland are hot spots of ARGs. However, few studies have investigated the on-site occurrence of ARGs distributed in the process of anaerobic digestion (AD) followed by land application of swine wastewater. Two typical swine farms, in southern and northern China respectively, with AD along with land application were explored on ARG distributions. ARGs were highly abundant in raw swine wastewater, AD effectively reduced the copy number of all detected ARGs (0.21-1.34 logs removal), but the relative abundance with different resistance mechanisms showed distinctive variation trends. The reduction efficiency of ARGs was improved by stable operational temperature and longer solid retention time (SRT) of AD. ARGs in soil characterized the contamination from the irrigation of the digested liquor. The total ARGs quantity in soil fell down by 1.66 logs in idle period of winter compared to application period of summer in the northern region, whereas the total amount was steady with whole-year application in south. Some persistent (sul1 and sul2) and elevated ARGs (tetG and ereA) in AD and land application need more attention.

A novel integrated step-feed biofilm process for the treatment of decentralized domestic wastewater in rural areas of China.

For wastewater treatment in rural areas, a novel three-stage step-feed wastewater treatment system, combined with a drop-aeration biofilm process, was tested in the laboratory to investigate its performance in removing suspended solids (SS), chemical oxygen demand (COD), NH4(+)-N, total nitrogen (TN), and total phosphorus (TP). The removal rates of SS, COD and NH4(+)-N were 90%, 80%, and 90% in effluent concentrations less than 10 mg/L, 50 mg/L and 8 mg/L, respectively. The TP removal rate was less satisfactory. The C/N ratio in the raw wastewater was often less than 3.5, and the removal efficiency of TN was therefore limited. A carbon-release batch experiment was carried out to measure the feasibility of enhancing denitrification at low influent C/N ratios. The result showed that the C/N could be over 9.0 in the supernatant. Polymerase chain reaction denaturing gradient gel electrophoresis technology was used to reveal the changes in the bacterial community during different stages of the integrated step-feed biofilm process. The results showed that banding patterns and the distribution of dominant bands for the same experimental period in different aerobic zones were similar. Phylogenetic analysis indicated that lanes 10, 11 and 12, which presented three aerobic zones at the same operation period, had the closest phylogenetic relationship among the lanes.