Performance of Submerged Membrane Bioreactor for Domestic Wastewater Treatment

In the present research, a submerged membrane bioreactor was tested to treat domestic wastewater. Three experimental runs were conducted all with a hydraulic retention time of 5h and sludge retention times (SRTs) of 5, 10, and 20 d. The pollutant removal performance of the membrane bioreactor, the membrane effluent quality, and a kinetic model for sludge growth in the bioreactor were investigated. The combined process was capable of removing over 90% of both COD (chemical oxygen demand) and NH 3 N on the average. The total removal for COD was almost independent of SRT, but that for NH 3 N improved with increasing SRT. Membrane effluent quality meets the water quality standard for reuse issued by the Ministry of Construction of China. Increasing SRT causes the concentrations of suspended solids (SS) and volatile suspended solids (VSS) in the bioreactor to increase. However, the ratio of VSS/SS did not change much. Kinetic analysis showed that the sludge yield coefficient (kg VSS·kg COD -1 ) and the endogenous coefficient of microorganisms were 0.25 and 0.04d -1 , which are similar to those of the conventional activated sludge process.

Improving biodegradation potential of domestic wastewater by manipulating the size distribution of organic matter

Carbon source is a critical constraint on nutrient removal in domestic wastewater treatment.However,the functions of particulate organic matter（POM） and some organics with high molecular weight（HMW） are overlooked in the conventional process,as they cannot be directly assimilated into cells during microbial metabolism.This further aggravates the problem of carbon source shortage and thus affects the effluent quality.Therefore,to better characterize organic matter（OM） based MW distribution,microfiltration/ultrafiltration/nanofiltration（MF/UF/NF） membranes were used in parallel to fractionate OM,which obtained seven fractions.Hydrolysis acidification（HA） was adopted to manipulate the MW distribution of dissolved organic matter（DOM） and further explore the correlation between molecular size and biodegradability.Results showed that HA pretreatment of wastewater not only promoted transformation from POM to DOM,but also boosted biodegradability.After 8 hr of HA,the concentration of dissolved organic carbon（DOC） increased by 65%,from the initial value of20.25 to 33.48 mg/L,and the biodegradability index（BOD5（biochemical oxygen demand）/SCOD（soluble chemical oxygen demand）） increased from 0.52 to 0.74.Using MW distribution analysis and composition optimization,a new understanding on the characteristics of organics in wastewater was obtained,which is of importance to solving low C/N wastewater treatment in engineering practice.

Phosphate adsorption performance of a novel filter substrate made from drinking water treatment residuals

Phosphate is one of the most predominant pollutants in natural waters. Laboratory experiments were conducted to investigate the phosphate adsorption performance of a（NFS） made from drinking water treatment residuals. The adsorption of phosphate on the NFS fitted well with the Freundlich isotherm and pseudo second-order kinetic models. At p H 7.0, the maximum adsorption capacity of 1.03 mg/g was achieved at 15°C corresponding to the wastewater temperature in cold months, and increased notably to 1.31 mg/g at 35°C.Under both acidic conditions（part of the adsorption sites was consumed） and basic conditions（negative charges formed on the surface of NFS, which led to a static repulsion of PO43-and HPO42-）, the adsorption of phosphate was slightly inhibited. Further study showed that part of the adsorption sites could be recovered by 0.25 mol/L Na OH. The activation energy was calculated to be above 8.0 k J/mol, indicating that the adsorption of phosphate on NFS was probably a chemical process. Considering the strong phosphate adsorption capacity and recoverability, NFS showed great promise on enhancing phosphate removal from the secondary treated wastewater in the filtration process.