Abstract
The filling ratio (FR) of a carrier has an influence on the pollutant removal of the aerobic moving bed biofilm reactor (MBBR). However, the effect of the polyethylene (PE) carrier FR on the performance and microbial characteristics of the denitrifying MBBR for the treatment of wastewater treatment plant (WWTP) effluent has not been extensively studied. A bench-scale denitrifying MBBR was set up and operated with PE carrier FRs of 20%, 30%, 40%, and 50% for the degradation of chemical oxygen demand (COD) and nitrogen from WWTP effluent at 12 h hydraulic retention time (HRT). The nitrate removal rates with FRs of 20%, 30%, 40%, and 50% were 94.3 ± 3.9%, 87.7 ± 7.3%, 89.7 ± 11.6%, and 94.6 ± 4.0%, and the corresponding denitrification rates (rNO3--N) were 8.0 ± 5.6, 11.3 ± 4.6, 11.6 ± 4.6, and 10.0 ± 4.9 mg NO3−-N/L/d, respectively. Nitrous oxide reductase (nosZ) gene-based terminal restriction fragment length polymorphism (T-RFLP) analysis illustrated that the highest functional diversity (Shannon’s diversity index, H′) of biofilm microbial community was obtained at 30% FR. The quantitative polymerase chain reaction (qPCR) results indicated that the abundance of nitrate reductase (narG) and nosZ genes at 30% FR was significantly higher than that at 20% FR, and no significant changes were observed at 40% and 50% FRs. Thus, 30% FR was recommended as the optimal carrier FR for the denitrifying MBBR.
Highlights
High total nitrogen (TN) of wastewater treatment plant (WWTP) effluent is always the primary factor affecting its compliance with the discharge standards and recycling, because the TN standard for WWTP effluent (Class I-A, 15 mg·L−1, SEPA of China, 2002) [1] is much higher than the maximum required TN value of natural surface water (Class V, 2.0 mg/L−1, SEPA of China, 2002) [2]
WWTP effluent always has low organic content and low carbon-to-nitrogen ratio (C/N), and it perhaps contains lead and zinc ions caused by the dissolution of minerals [4,5], which results in the complexity of WWTP effluent denitrification and nitrogen removal
The chemical oxygen demand (COD) removal efficiency increased with the increase of filling ratio (FR), and all the effluent COD met the Class I(A) requirement of the Discharge Standard of Pollutants for Municipal WWTP in China (GB18918-2002) [1], i.e., less than 50 mg L−1
Summary
High total nitrogen (TN) of wastewater treatment plant (WWTP) effluent is always the primary factor affecting its compliance with the discharge standards and recycling, because the TN standard for WWTP effluent (Class I-A, 15 mg·L−1 , SEPA of China, 2002) [1] is much higher than the maximum required TN value of natural surface water (Class V, 2.0 mg/L−1 , SEPA of China, 2002) [2]. It is very urgent to further remove the TN from WWTP effluent for the production of high-quality recycled water, which can be used as recharge water for rivers or groundwater in water shortage areas. WWTP effluent always has low organic content and low carbon-to-nitrogen ratio (C/N), and it perhaps contains lead and zinc ions caused by the dissolution of minerals [4,5], which results in the complexity of WWTP effluent denitrification and nitrogen removal. Public Health 2019, 16, 3244; doi:10.3390/ijerph16183244 www.mdpi.com/journal/ijerph
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