Abstract
A new multi-point inflow pre-anoxic/oxic/anaerobic/anoxic/oxic (A1/O2/A3/A4/O5) sludge-membrane coupling process and pilot plant were developed and designed to solve the problem of nitrogen and phosphorus removal of low carbon and nitrogen (C/N) ratio domestic sewage in southern China. The removal effect and transformation rule of organic matter, nitrogen, and phosphorus in the system were studied by changing the distribution ratio of multi-point influent. The average C/N ratio of the influent was 2.09 and the influent distribution ratio was 1:1. When the temperature was 16-25 °C, the average concentrations of chemical oxygen demand (COD), ammonia nitrogen (NH4+- N), total nitrogen (TN), and total phosphorus (TP) in the effluent were 21.31 (±2.65), 0.60 (±0.24), 12.76 (±1.09), and 0.34 (±0.05) mg/L, respectively, and their average removals are 87.3 (±1.2)%, 98.7 (±0.4)%, 74.1 (±1.3)%, and 88.1 (±0.4)% respectively. When the low temperature was 12-15 °C, the average removals were 78.6 (±1.1)%, 90.5 (±1.3)%, 73.7 (±1.13)%, and 86.6 (±1.7)%, respectively. Compared with the traditional anaerobic/anoxic/aerobic (A2O) process under the same conditions, the TN removal was increased by 15.4%, and the TP removal was increased by 22.2%. This system has obvious advantages in treating wastewater with low C/N ratio, thereby solving the problem wherein the effluent of biological phosphorus removal from low C/N ratio domestic sewage was difficult when it was lower than 0.5 mg/L.
Highlights
With the problem of water eutrophication becoming more and more serious, the standard of nitrogen and phosphorus emission is becoming more and more strict (Zhang et al 2017)
This system has obvious advantages in treating wastewater with low carbon and nitrogen ratio, which solved the problem that the effluent of biological phosphorus removal from low C/N ratio domestic sewage was difficult to be lower than 0.5 mg/L
It is considered that the raw water first entered the preanoxic (A1) and anaerobic (A3) stages, most of the COD in influent would be consumed by anaerobic phosphorus release and anoxic denitrification as electron donor, which resulted in that different proportion of multi-point influent had basically no influence on COD removal, which was basically consistent with the conclusion of Wang et al 's study on the effect of nitrogen and phosphorus removal in multi-stage AO system through different influent methods(Abyar et al 2018; Wang et al 2018)
Summary
With the problem of water eutrophication becoming more and more serious, the standard of nitrogen and phosphorus emission is becoming more and more strict (Zhang et al 2017). Nan et al (2018) Enhanced the denitrification and phosphorus removal of DPAOs in the improved A2O-BAF double sludge system by step-feeding, so as to realize the effective utilization of carbon source in the system, it still could not solve the contradiction between denitrifying bacteria and phosphorus accumulating bacteria for carbon source competition, and backwashing would consume a lot of water. Peng and Ge (2011) Successfully enhanced the SND effect of the system by controlling the lower DO concentration in the aerobic stage and increasing the sludge concentration in the step-feeding process, which enhanced the utilization rate of carbon source in the system. Especially for low C/N ratio domestic sewage, the contradiction between organic matrix competition and SRT is prominent, which seriously limits the further improvement of nitrogen and phosphorus removal efficiency (Deng et al 2016). It is urgent to optimize and upgrade the traditional A2O process
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