Bioaugmentation In Constructed Wetlands Treating Rural Domestic Wastewater

At present China’s rural environmental faces a heavy pollution. Rural domestic wastewater needs to be treated imminently. Constructed wetlands (CWs) have a broad application and have been widely used in the developing countries, because of their lower cost, less operation and maintenance requirements, and lack of reliance on energy inputs. Microbial uptake and degradation is the main process to pollutants removal in the CWs. Bioaugmentation, being an economical and eco-friendly approach, has emerged as the most advantageous wastewater clean-up technique for contaminated sites. It is usually achieved by inoculating microbial strains or mixes of strains that are isolated from the same polluted site and grown in the selective media containing the pollutant to enhance microbial activities in removing undesired pollutants. The successful use of bioaugmentation in CWs makes good sense, saving water rescourse, achieving water recycling, making the use of rural water development continuely.In this study, six denitrifying bacteria were chosen and formed four different microbial flora groups. The suitable concentration of four microbial flora groups for wastewater treatment was investigated. The longterm treatment performance in the constructed wetlands microcosm (CWMs) for treating domestic wastewater (DW) and polluted river water (RW) was studied, and the contaminant transformation and degradation characteristics during removal process were also investigated. The effects of bioaugmentation in CWMs treating simulated DW and RW were also studied. The pilot-scale CWs were conducted and the two-year treatment performance of CWs were evaluated. The main pollutant of rural domestic wastewater in practice, such as chemical oxyen demand (COD), total nitrogen (TN), ammonia (NH3-N), total phosphorus (TP) removal was investigated in CWs at different time introduced by Paenibacillus sp. XP1. The optimal HRT for pollutants achieving the GB18918-2002standard (China) for Class I-B guideline and the period of repeated inoculation were also investigated. The main research conclusions are as follows: (1) The six strains were found to have a good effect on nitrogen removal and could be used as the CWs inoculated microbial flora. Their denitrifying gas products were verified to be N2and there was no greenhouse gases appeared. It was shown that they had good environmental benefits if they were chosen for bioaugmentation. All the four microbial flora groups were highly efficient on N removal.1%concentration of F4group (conclude with six strains) was chosed for the most suitable group for inoculation in CWs. At the time of144h, N was completely removed by F4group.(2) The lab-scale CMWs had good purification effect for simulated domestic wastewater (DW) and polluted river water (RW). In the RW test, the average effluent concentration of COD and NH3-N did not met Grade-Ⅲ of national surface water standards in China (GB3838-2002), and the average removal efficiency of COD, NH3-N, TN and TP was42%to60.3%,35%to45%,23.7%to33.2%and13%to25%. In the DW test, the average effluent concentration of COD and NH3-N did not achieve the GB18918-2002standard (China) for Class I-B guideline, and the average removal efficiency of COD, NH3-N, TN and TP was61%to68.7%,37.5%to66.7%,27.4%to45.5%and50%to63.7%.(3) Nutrient removal in CMWs planted with Phragmites and inoculated with a consortium of six denitrifying bacteria was evaluated as a possible treatment for polluted river water (RW) and domestic wastewater (DW) in northern China. Experiments were conducted using the batch-loaded method over a15-day period. Biol (RW with Phragmites inoculated with the bacterial consortium) and Abiol (DW with Phragmites and bacterial inoculation) showed significant improvement in chemical oxygen demand (CODcr), total nitrogen (TN), ammonia (NH3-N) and total phosphorus (TP) removal efficiency compared with Bio2and Abio2, i.e., Phragmites without bacteria inoculation. On the7th day, the removal efficiencies of Biol were found to be75.7%for CODcr,96.7%for TN,96.8%for NH3-N and90.4%for TP in RW microcosms, and85.7%for CODcr,75%for TN,88.6%for NH3-N and88%for TP in Abiol DW microcosms. Optimal hydraulic retention time (HRT) was7days.(4) CWs were conducted in Shandong Architectural University, based on the secondary effluent water treatment station with the capacity of2.0m3/d in this study. The influent water quality met the water quality characteristics of typical sewage. TN concentration in the influent was relatively high with the main component was NH3-N. COD changed with the seasons, TP concentrations was low. In the effluent the main pollutant COD, NH3-N, TP could not or stability to achieve the GB18918-2002standard (China) for Class I-B guideline.(5) Bioaugmentation with Paenibacillus sp. XP1in CWs had good effect on pollutant removal. Two CWs planted with Typha orientalis (CCW) and Phragmites (RCW) was constructed to study the effect of the addition of Paenibacillus sp. XP1on nitrogen removal of rural domestic wastewater in autumn (15-21℃). CCW inoculated by Paenibacillus sp. XP1(CCW-XP1) had obvious improvement on NH3-N and TN removal efficiency than RCW-XP1. The removal efficiency of TN in the CCW is similar to that of NH3-N, and the maximal removal efficiency of78%was achieved, doubled with the control group. The final removal efficiencies of the CCW-XP1were found to be73%for chemical oxygen demand (COD),94%for NH3-N and78%for TN. The effect of HRT variation on treatment efficiency of CCW was also discussed. Statistical analyses indicated that the optimal HRT for NH3-N concentrations achieving the GB18918-2002standard (China) for Class I-B guideline of8.0mg/L were4days, while the NH3-N removal of the control group had not meet the criteria until18days. In comparison with the control group, HRT of CCW-XP1was shortened for more than15days. The CCW would be a cost-effective measure for N removal of rural domestic wastewater by bioaugmentation. In this study, N removal in a pilot scale CW planted with Phragmites inoculated with Paenibacillus sp. XP1was evaluated as a possible treatment for the secondary effluent of rural DWfrom sewage disposal system in summer (28-35℃) and autumn (15-21℃) before harvesting in northern China. Experiment was conducted using the batch-loaded method over a17day period. RCW-XP1(CW with Phragmites inoculated with Paenibacillus sp. XP1inoculation) in summer and autumn stages shows obvious decreases in CODcr, and increases in NH3-N and TN removal compared with RCW (CW with Phragmites without bacterial inoculation). Four days after treatments were set up, removal efficiencies of RCW-XP1were found to be76.2%for CODcr,83%for NH3-N and63.8%for TN in summer, and69.5%for CODcr,76.9%for NH3-N and55.6%for TN in autumn. Optimal hydraulic retention time (HRT) was4days.(6) Compared with the traditional biological treatment, CWs costs were lower. The treatment was cost about1yuan/ton when the effluent of conventional sewage treatment plant sewage reached reuse standards. The average power cost was less than0.01yuan/ton when using decentralized rural CWs. Bioaugmentation in CWs were cost about0.23to0.29yuan/ton in total which was1/4-1/5of in sewage plant treatment.