For meeting wastewater reuse standards with kinds of wastewaters, the new physic-chemical and biological technology is developed and integrated in order to solve some technical issues of wastewater treatment facilities in practice, such as large occupied land area, unstable operation, low purification efficiency, high treatment costs. Therefore the integration systems of physico-chemical and biological wastewater treatment processes are built up, and applied in projects and demonstration projects of wastewater treatment and reclamation at different scales.

(1) Development and integration for biological wastewater treatment and reclamation

According to principles for oxidation ditch wastewater treatment, a new integrated oxidation ditch process with vertical circulation (IODVC) and its equipment are invented. Due to adopting vertical circulation, this process and equipment can realize automatic return of activated sludge, and its settlement zone has no impact on the flow mode of intermixtures in the oxidation ditch. Therefore the IODVC may save about 50% of occupied land area, and 30% of running costs, compared with conventional integrated oxidation ditch. High removal efficiencies of organic pollutants, ammonium nitrogen and total nitrogen are reached, i.e. 95% of COD removal rate. In consideration of large energy consumption and high running costs for side-stream membrane bioreactor and submerged membrane bioreactor with suction pump, a new membrane bioreactor (MBR) with gravity drain is researched and developed. The membrane flux of the MBR is continuously obtained with gravity. This MBR not only has the same advantages as the side-stream membrane bioreactor and submerged membrane bioreactor with suction pump, i.e. high efficiency of pollutant removals, but also can ameliorate membrane fouling because of no need of pumps and complicated membrane washing equipment. Compared with side-stream membrane bioreactor and submerged membrane bioreactor with suction pump, this kind of membrane bioreactor with gravity drain has advantages as follows: few footprint due to compact structure, low energy consumption (saving more than 2/3), easy operation and maintenance, few capital and operational costs. Moreover, the treated water can meet the national standard of wastewater treatment and reclamation (GB/T 18920-2002) if the effluent of this MBR is treated by advanced treatment processes. Such treated water can be used to flush toilets, green environment, recharge the cooling water used in industries. For the stench generated during the wastewater treatment process, the complex biological odors abatement technology and equipment is investigated and developed to online treat odors emitted during the wastewater treatment process. Usually, substances contained in emitting odors mainly include H2S, NH3, and volatile organic substances. The combined biological odors abatement reactor may remove efficiently both hydrophilic and hydrophobic pollutants in the same time, and the removal rate of odors is above 90%. The sludge reduction induced by predator is researched to develop a novel bioreactor for sludge reduction. In summary, technologies of biological wastewater treatment, odor treatment and sludge reduction are optimized and combined to form an integrated and cost-effective system for wastewater treatment system of high-efficient cleaning for residential district wastewater treatment. This kind of integrated system has been successfully used in practice such asfood & beverage waste treatment and resue projects.

(2) Development and integration of physico-chemical and biological wastewater treatment processes for wastewater treatment and reuse

On the basis of wastewater characteristics of residential districts around oilfields and requirements of water quality for recharging water into oilfield, biological wastewater treatment, coagulative precipitation, sand filtration and disinfection are screened and integrated to form a cost-effective wastewater treatment and reuse process (bio-contact oxidation-coagulation-precipitation-sand filtration-disinfection) for oilfield. Aiming at reusing wastewater collected in the residential districts of Daqing Oilfield, the challenge of this project is to solve both requirements for stabilizing operation of wastewater treatment and reuse facilities and special requirements for recharging water into oilfield at low temperature. In addition, the quality of the treated water such as oil concentration, suspended solids, biostability, must be in accord with requirements of recharge water into oilfield in the cold weather. Due to long freezing period (about 6 months) in Daqing, the temperature of wastewater collected from residential districts in the winter is close to zero centigrade degree. Hence how to assure stable operation and high purification of biological wastewater treatment process in the winter is a big challenge because there is no precedent as reference. Based on literature survey and experimental investigation, it is found that the most aspect affected by the low temperature is how to efficiently remove colloidal organic compounds in wastewater. At the low temperature, even as low as 4℃, 80% of soluble COD in the wastewater can be removed by the biological treatment methods. For the residual organic compounds with colloidal form, the subsequent coagulative precipitation can remove them and thus assure the high removal efficiency of organic pollutants. Such successful engineering experience provides valuable reference for wide application of wastewater treatment and reuse in frigid regions.

Considering current situation of limited land source and its expensive costs in Beijing, compact equipment is developed for wastewater treatment and reuse in residential districts, and is interacted with aerobic process and filtration. This kind of equipment can solve some problems arose from grey water reuse, such as complicated equipment, large land area, unstable operation, and has been successfully used in grey water treatment and reuse in practice. Its effluent quality can meet with the standards of wastewater treatment and reuse (GB/T 18920-2002).

Based on the climatic and geographical features in the South of China, a high-efficient system is developed through integrating whirling flocculation, air floatation and biofilter processes. It has been successfully applied in a demonstration project for wastewater treatment and reuse in local residential community, through combining of enhanced flocculation and biofiltration in the wastewater treatment and reuse. The quality of the treated water can meet with the standard of wastewater treatment and reuse (GB/T 18920-2002).