Nature-based solutions for rural wastewater and agricultural waste management

Abstract

For small communities in rural settings, nature-based, passive treatment systems such as constructed wetlands (CWs) provide alternatives to energy and chemical intensive centralised treatment works. However, there is insufficient information on CW performance across the seasons and wide range of environmentally relevant water quality parameters. Fieldwork was conducted at Northumbrian Water’s sewage treatment plant (STP) at Birtley, England, which co-treats abandoned coal mine and STP effluents in CWs. This site represents a unique treatment challenge as it requires simultaneous removal of metals, nutrients, and pathogens. STP and coal mine effluent, CW influent and effluent, and receiving river water samples were comprehensively analysed for chemical and microbial quality in different seasons, followed by multivariate data analysis. Overall, chemical quality of the CW effluent was comparable to the river water. The CWs showed efficient removal of phosphate and iron and successfully converted treated sewage and mine water microbiomes into a freshwater microbiome. However, horizontal flow CWs require large land areas. It was therefore investigated if the performance of small-scale vertical flow CWs (biofilter) containing sand as biofilter medium could be improved by activated carbon (AC) amendment. It was found that 5% w/w AC-amendment in sand effectively removed putative human pathogens and micropollutants like diuron, diclofenac and enrofloxacin. Biochar is an AC-like material produced from agricultural waste biomass. Extending the lessons learned from nature-based wastewater management towards agricultural fields, this study tested the hypothesis that combined application of renewable energy generation by-products anaerobic digestate and coconut husk (CH) biochar can improve soil nutrient conditions, whilst minimizing groundwater pollution risks. Microcosms simulated digestate application to agricultural soil with and without CH biochar. Molecular microbiology techniques demonstrated that CH biochar retarded nitrate leaching via slower nitrification in digestate-amended soil. All these findings will contribute towards development of a more sustainable and circular rural economy.