The cotreatment of old landfill leachate and domestic sewage in rural areas by deep subsurface wastewater infiltration system (SWIS): Performance and bacterial community

In this work, two deep subsurface wastewater infiltration systems (SWISs) were constructed and fed with domestic sewage (control system, S1) and mixed wastewater consisting of old landfill leachate and domestic sewage (experimental system, S2). S1 and S2 exhibited favorable removal efficiencies, with TP (98.8%, 98.7%), COD (87.6%, 86.9%), NH4+-N (99.8%, 99.9%) and TN (99.2%, 98.9%). Even when increasing the pollutant load in S2 by adding old landfill leachate, the almost complete removal performance could be maintained in terms of low effluent concentrations and even increased in terms of load removal capabilities, which included COD (19.4, 25.9 g.m(-2).d(-1)), NH4+-N (8.2, 19.9 g.m(-2).d(-1)), TN (8.9, 20.6 g.m(-2).d(-1)). To investigate the transformation of dissolved organic matter along depth, Three-Dimensional Excitation Emission Matrix fluorescence spectroscopy combined with Fluorescence Regional Integration analysis was applied. The results showed that P-I,P- n and P-II,P- n (the proportions of biodegradable fractions) increased gradually from 6.59% to 21.8% at S2_20 to 10.8% and 27.7% at S2_110, but P-III,P- n and P-nu,P- n (the proportions of refractory organics) declined from 23.1% to 27.8% at S2_20 to 21.1% and 16.4% at S2_110, respectively. In addition, high-throughput sequencing technology was employed to observe the bacterial community at different depths, and the predicted functional potential of the bacterial community was analyzed by PICRUSt. The results showed that the genera Flavobacterium, Pseudomonas, Vogesella, Acinetobacter and Aquabacterium might be responsible for refractory organic degradation and that their products might serve as the carbon source for denitrifiers to achieve simultaneous nitrate and refractory organic removal. PICRUSt further demonstrated that there was a mutual response between refractory organic degradation and denitrification. Overall, the combined treatment of domestic sewage and old leachate in rural areas by SWIS is a promising approach to achieve comprehensive treatment. (C) 2020 Elsevier Ltd. All rights reserved.

Automated summary

The study on two deep subsurface wastewater infiltration systems demonstrates that even with an increased pollutant load from old landfill leachate, favorable removal efficiencies can be maintained and even increased. Fluorescence spectroscopy analysis shows an increase in the proportion of biodegradable fractions and a decrease in refractory organics. High-throughput sequencing technology and PICRUSt analysis suggest that certain bacterial genera may play a key role in the degradation of refractory organics and denitrification processes.