Diatomite Precoated Nonwoven Membrane Bioreactor for Domestic Wastewater Reclamation

Nonwoven was selected as filtration materials in submerged membrane bioreactor( MBR) for domestic wastewater reclamation. For its hydrophobic membrane surface,diatomite was precoated on nonwoven to improve membrane hydrophilicity. In the precoating stage,diatomite dynamic membrane could be formed on10 μm polyethylene nonwoven surface efficiently and effluent turbidity could be below 5 nephelometric turbidity units( NTU).The MBR system was operated steadily under gravity flow and scanning electron microscope( SEM) analysis showed that nonwoven membrane was only partially fouled at the membrane flux of 5 L/( m2·h). Average removal efficiencies of chemical oxygen demand( COD) and NH +4-N were above 86 % and 50 %,respectively. The effluent turbidity and chromaticity were below 5 NTU and 25°,respectively. Those results could meet the requirements for wastewater reuse.

Suitability Evaluation for the Construction of Decentralized Wastewater Reclamation Facilities in Beijing

水资源的缺乏使越来越多的城市和城区开始使用中水作为额外的经济合理的供水水源,并为此制定相应政策。然而,不适宜的中水利用政策往往对用水户使用再生水产生不利影响。本研究目的在于评价中水设施建设适宜性并分析不同行业的中水利用适宜情况,为制定或修订中水利用政策提供参考。本研究以北京市为研究区,在中水生产成本影响因素分析基础上,得到了中水设施建设限制因素和中水设施建设适宜条件,并对北京市机关、高校、饭店的用水户进行了适宜性评价。本研究结果表明,运行水量对中水生产成本有决定性影响。有效原水量对应的给水量、有效中水需求量、建筑面积适合作为中水设施建设影响因素,它们的下限可作为中水设施建设适宜条件。本研究通过分析北京市部分机关、高校、饭店用水户的用水情况,得到这些行业的中水设施建设适宜条件,并用于适宜性评价。评价结果表明,大部分机关用水户和大部分一、二星级饭店不适宜建设中水设施,而大部分高校和大部分三星级以上饭店适宜建设中水设施。

Changes of microbial composition during wastewater reclamation and distribution systems revealed by high- throughput sequencing analyses

This study employed 454-pyrosequencing to investigate microbial and pathogenic communities in two wastewater reclamation and distribution systems. A total of 11972 effective 16S rRNA sequences were acquired from these two reclamation systems, and then designated to relevant taxonomic ranks by using RDP classifier. The Chao index and Shannon diversity index showed that the diversities of microbial communities decreased along wastewater reclamation processes, eroteobacteria was the most dominant phylum in reclaimed water after disinfection, which accounted for 83% and 88% in two systems, respectively. Human opportunistic pathogens, including Clostridium, Escherichia, Shigella, Pseudomonas and Mycobacterium, were selected and enriched by disinfection processes. The total chlorine and nutrients （TOC, NH3-N and NO3-N） significantly affected the microbial and pathogenic communities during reclaimed water storage and distribution processes. Our results indicated that the disinfectant-resistant pathogens should be controlled in reclaimed water, since the increases in relative abundances of pathogenic bacteria after disinfec- tion implicate the potential public health associated with reclaimed water.

Growth and Repair Potential of Three Species of Bacteria in Reclaimed Wastewater after UV Disinfection

Objective The growth and repair potential of three typical microorganisms in reclaimed water after UV disinfection was investigated to assess the effects of photo-reactivation and dark repair of microorganisms,and the microbial safety of reclaimed water following this procedure.Methods The growth and repair potential of Escherichia coli,a fecal coliform strain and Bacillus subtilis in the effluent of a biological wastewater treatment plant disinfected by a low-pressure UV lamp were investigated.Results Any increase in bacterial numbers in the effluent after UV disinfection was due to damage repair.Exposure to photo-reactivating light for 8-10 h after UV irradiation with a dose of 5 mJ/cm 2,the highest percentage of photo-reactivation observed for E.coli and the fecal coliform strain was 29% and 15% respectively.B.subtilis showed little photo-reactivation under these conditions.The percentage of photo-reactivation was related to the UV dose and the photo-reactivating time,and a function was developed to forecast the final concentrations of E.coli and the fecal coliform strain after UV disinfection with possible photo-reactivation.Conclusion Different species of bacteria displayed different responses to UV light and different repair potentials.The repair of indigenous bacteria in wastewater needs to be investigated in future work.

Analysis of Circumstance Influence Factors on HMBR for Waste-water Reclamation in Dwelling District

Circumstance influence factors on Hybrid Membrane Bio-Reactor (HMBR) process for the wastewater reclamation in dwelling district was analyzed. The main characteristic of this process is that sludge and nitrified effluent can be recycled automatically, which simplifies the operation of system and is beneficial to get the high removal of organics and nitrogen. Based on the analysis of circumstance influence factors, it is recommended that water temperature of about 20℃, influent pH of 6 -7 and DO of 1. 0 mg/L - 1. 5 mg/L in the aerobic compartment. Under these conditions, COD, BOD5, NH4+ -N, and TN were removed effectively in HMBR and the average removal efficiencies were 94.5%, 99.3%, 99.4% and 84.7%, respectively. SS and coliforms were both below the detection limits in the permeate of UF membrane module, and turbidity was less than 1NTU. The treated effluent meets the Miscellaneous Domestic Water Quality Standard (CJ25.1-89), and can be reused multipurposely such as watering of green belts, cleaning and toilet flushing water after disinfection.

Toxicity-based assessment of the treatment performance of wastewater treatment and reclamation processes

The reclamation and reuse of wastewater is one of the possible ways to relieve the serious fresh water resource crisis in China. Efficient reclamation treatment technologies ensure the safe reuse of reclaimed water. In order to screen out and evaluate technologies appropriate for reclamation treatment, a great deal of efforts have been brought to bear. In the present study, a toxicity-based method including a Photobacterium phosphoreum test for acute toxicity and SOS/umu test for genotoxicity, accompanied by the traditional physicochemical parameters DOC （dissolved organic carbon） and UV254 （absorbance at 254 nm）, was used to measure the treatment performance of different reclamation processes, including the anaerobic-anoxic-oxic biological process （A^2O） and subsequent physical/chemical reclamation processes （ultrafiltration, ozonation, chlorination）. It was found that for the secondary effluent after the Aao process, both the toxicity and physicochemical indices had greatly decreased compared with those of the influent. However, chemical reclamation processes such as ozonation and chlorination could possibly raise toxicity levels again. Fortunately, the toxicity elevation could be avoided by optimizing the ozone dosage and using activated carbon after ozonation. It was noted that by increasing the ozone dosage to 10 mg/L and employing activated carbon with more than 10 min hydraulic retention time, toxicity elevation was controlled. Furthermore, it was shown that pre-ozonation before activated carbon and chlorination played an important role in removing organic compounds and reducing the toxicity formation potential. The toxicity test could serve as a valuable tool to evaluate the performance of reclamation processes.

Formation potentials of typical disinfection byproducts and changes of genotoxicity for chlorinated tertiary effluent pretreated by ozone

The effects of ozonation on the formation potential of typical disinfection byproducts （DBPs） and the changes of genotoxicity during post chlorination of tertiary effluent from a sewage treatment plant were investigated. Ozonation enhanced the yields of all detected chlorine DBPs except CHCI3. At a chlorine dose of 5 mg/L, the three brominated THMs and five HAAs increased, while chloroform decreased with the increase of ozone dose from 0 to 10 mg/L （ozone dose in consumption base）. At a chlorine dose of 10 mg/L, the two mixed bromochloro species THMs and two dominant HAAs （DCAA and TCAA） increased firstly and then decreased with the increase of ozone dose, with the turning point approximately occurring at an ozone dose of 5 mg/L. The genotoxicity detected using umu test, on the other hand, was removed from 7 Ixg 4-NQO/L to a negligible level by ozonation under an ozone dose of 5 mg/L. Chlorination could further remove the genotoxicity to some extent. It was found that SUVA （UV absorbance divided by DOC concentration） might be used as an indicative parameter for monitoring the removal of genotoxicity during the oxidation.

Development and application of some renovated technologies for municipal wastewater treatment in China

China has been experiencing fast economic development in recent decades at the cost of serious environ-mental deterioration.Wastewater discharge,especially municipal wastewater discharge,and non-point pollution sources are becoming the major water pollution source and research focus.Great efforts have been made on water pollu-tion control and a number of renovated technologies and pro-cesses for municipal wastewater treatment and reclamation as well as non-point pollution control have been developed and applied in China.This paper discusses the development and application of the appropriate technologies,including natural treatment systems,anaerobic biological treatment,biofilm reactors and wastewater reclamation technologies,for water pollution control in the country.

Advanced treatment of municipal wastewater by nanofiltration： Operational optimization and membrane fouling analysis

Municipal sewage from an oxidation ditch was treated for reuse by nanofiltration（NF） in this study. The NF performance was optimized, and its fouling characteristics after different operational durations（i.e., 48 and 169 hr） were analyzed to investigate the applicability of nanofiltration for water reuse. The optimum performance was achieved when transmembrane pressure = 12 bar, p H = 4 and flow rate = 8 L/min using a GE membrane. The permeate water quality could satisfy the requirements of water reclamation for different uses and local standards for water reuse in Beijing. Flux decline in the fouling experiments could be divided into a rapid flux decline and a quasi-steady state. The boundary flux theory was used to predict the evolution of permeate flux. The expected operational duration based on the 169-hr experiment was 392.6 hr which is 175% longer than that of the 48-hr one. High molecular weight（MW） protein-like substances were suggested to be the dominant foulants after an extended period based on the MW distribution and the fluorescence characteristics. The analyses of infrared spectra and extracellular polymeric substances revealed that the roles of both humic- and polysaccharide-like substances were diminished, while that of protein-like substances were strengthened in the contribution of membrane fouling with time prolonged. Inorganic salts were found to have marginally influence on membrane fouling. Additionally, alkali washing was more efficient at removing organic foulants in the long term, and a combination of water flushing and alkali washing was appropriate for NF fouling control in municipal sewage treatment.

Controlling various contaminants in wastewater effluent through membranes and engineered wetland

For effective wastewater reclamation and water recovery,the treatment of natural and effluent organic matters(NOM and EfOM),toxic anions,and micropollutants was considered in this work.Two different NOM(humic acid of the Suwannee River,and NOM of US and Youngsan River,Korea),and one EfOM from the Damyang wastewater treatment plant,Korea,were selected for investigating the removal efficiencies of tight nanofiltration(NF)and ultrafiltration(UF)membranes with different properties.Nitrate,bromate,and perchlorate were selected as target toxic anions due to their well known high toxicities.Tri-(2-chloroethyl)-phosphate(TCEP),oxybenzone,and caffeine,due to their different K_(ow) and pK_(a) values,were selected as target micropollutants.As expected,the NF membranes provided high removal efficiencies in terms of all the tested contaminants,and the UF membrane provided fairly high removal efficiencies for anions(except for nitrate)and the relatively hydrophobic micropollutant,oxybenzon.Through the wetlands,nitrate was successfully removed.Therefore,a fair process of combining membranes with an engineered wetland could be proposed for sustainable wastewater reclamation and optimum control of contaminats.

Sequential use of ultraviolet light and chlorine for reclaimed water disinfection

Several disinfection processes of ultraviolet （UV）, chlorine or UV followed by chlorine were investigated in municipal wastewater according to the inactivation of Escherichia coli, Shigella dysenteriae and toxicity formation. The UV inactivation of the tested pathogenic bacteria was not affected by the quality of water. It was found that the inactivated bacteria were obviously reactivated after one day in dark. Fluorescent light irradiation increased the bacteria repair. The increase of UV dosage could cause more damage to bacteria to inhibit bacteria self-repair. No photoreactivation was detected when the UV dose was up to 80 mJ/cm2 for E. coli DH5ct, and 23 mJ/cm2 for S. dysenteriae. Nevertheless, sequential use of 8 mJ/cm2 of UV and low concentration of chlorine （1.5 mg/L） could effectively inhibit the photoreactivation and inactivate E. coli below the detection limits within seven days. Compared to chlorination alone, the sequential disinfection decreased the genotoxicity of treated wastewater, especially for the sample with high NH3-N concentration.

Effect of different molecular weight organic components on the increase of microbial growth potential of secondary effluent by ozonation

Ozonation has been widely applied in advanced wastewater treatment. In this study, the effect of ozonation on assimilable organic carbon （AOC） levels in secondary effluents was investigated, and AOC variation of different molecular weight （MW） organic components was analyzed. Although the removal efflciencies were 47%-76% and 94%-100% for UV2s4 and color at ozone dosage of 10 mg/L, dissolved organic carbon （DOC） in secondary effluents was hardly removed by ozonation. The AOC levels increased by 70%-780% at an ozone dosage range of 1-10 mg/L. AOC increased significantly in the instantaneous ozone demand phase, and the increase in AOC was correlated to the decrease in UV254 during ozonation. The results of MW distribution showed that, ozonation led to the transformation of larger molecules into smaller ones, but the increase in low MW （〈1 kDa） fraction did not contribute much to AOC production. The change of high MW （〉100 kDa and 10-100 kDa） fractions itself during ozonation was the main reason for the increase of AOC levels. Furthermore, the oxidation of organic matters with high MWs （〉 100 kDa and 10-100 kDa） resulted in more AOC production than those with low MWs （1-10 kDa and 〈1 kDa）. The results indicated that removing large molecules in secondary effluents could limit the increase of AOC during ozonation.

Removal of fluorescence and ultraviolet absorbance of dissolved organic matter in reclaimed water by solar light

Storing reclaimed water in lakes is a widely used method of accommodating changes in the consumption of reclaimed water during wastewater reclamation and reuse. Solar light serves as an important function in degrading pollutants during storage, and its effect on dissolved organic matter（DOM） was investigated in this study. Solar light significantly decreased the UV_（254） absorbance and fluorescence（FLU） intensity of reclaimed water.However, its effect on the dissolved organic carbon（DOC） value of reclaimed water was very limited. The decrease in the UV_（254） absorbance intensity and FLU excitation–emission matrix regional integration volume（FLU volume） of reclaimed water during solar light irradiation was fit with pseudo-first order reaction kinetics. The decrease of UV_（254） absorbance was much slower than that of the FLU volume. Ultraviolet light in solar light had a key role in decreasing the UV_（254） absorbance and FLU intensity during solar light irradiation. The light fluence-based removal kinetic constants of the UV_（254） and FLU intensity were independent of light intensity. The peaks of the UV_（254） absorbance and FLU intensity with an apparent molecular weight（AMW） of 100 Da to 2000 Da decreased after solar irradiation, whereas the DOC value of the major peaks did not significantly change.