Innovative design of the biological wastewater treatment system

Abstract

A biological wastewater treatment system (BWTS), which composed of a 400 m2 biological wastewater treatment facility (BWTF) and a 100 m2 wetland landscaping lake, was designed to further treat the water quality of the recycling pond of an ecological sediment treatment plant of the Qingxi River in Qingxi Town, Dongguan City, Guangdong Province, China. BWTS was designed to treat the water of Class B of the Discharge standard of pollutants for municipal wastewater treatment plant (GB18918-2002) in the recycling pond into Class IV water of the Surface Water Environmental Quality Standard (GB3838-2002). The treatment capacity of BWTF was designed according to 1200 m3/d. The hydraulic load is 3m/d, volume load is 42 g (BOD)/(m3.d), and hydraulic retention time is 4 h. The inflow and outflow of BWTF were designed as the gravity flow without any power supply. The BWTF consists of active filtration facilities and plants with specific functions. The facility is capable of effectively filtering contaminants, especially with a very high removal efficiency of phosphorus (P) and nitrogen (N). The BWTF has five innovative outlet control systems that will be used to further reduce the nitrogen content to prevent algae growth. At the same time, the system can also remove pathogenic bacteria, heavy metals and hydrocarbons from the water, increase oxygen content in the water and reduce BOD. The wetland landscaping lake was designed to further treat the water quality and recycling use. The surplus water is discharged into the Qingxi River by a pipe. As compared with traditional wetland treatment, BWTS has the advantages of less land occupation, high efficiency, long service life, and low operation and maintenance costs. The structure of the BWTF is similar to the raingarden, however, they have different medium mixture ratio and inflow & outflow layouts. The water of the recycling pond is transferred to the BWTF through three underground pipes with a diameter of 150 mm, then the flow goes through the layers of protection, medium and gravel, and enters the nearby wetland landscaping lake by five outlet control manholes, an open canal and an underground pipe.