Decentralized wastewater treatment systems enable wastewater to be treated at the source for cleaner discharge into the environment, protecting public health while allowing for reuse for agricultural and other purposes. This study, conducted in Thailand, investigated a decentralized wastewater treatment system incorporating a physical and photochemical process. Domestic wastewater from a university campus and conventional septic tank effluent from a small community were filtered through a woven-fiber microfiltration (WFMF) membrane as pretreatment for ultraviolet (UV) disinfection. In domestic wastewater, WFMF reduced TSS (by 79.8%), turbidity (76.5%), COD (38.5%), and NO₃ (41.4%), meeting Thailand irrigation standards for every parameter except BOD. In septic tank effluent, it did not meet Thailand irrigation standards, but reduced TSS (by 77.9%), COD (37.6%), and TKN (13.5%). Bacteria (total coliform and Escherichia coli) and viruses (MS2 bacteriophage) passing through the membrane were disinfected by flow-through UV reactors containing either a low-pressure mercury lamp or light-emitting diodes (LEDs) emitting an average peak wavelength of 276 nm. Despite challenging and variable water quality conditions (2% < UVT < 88%), disinfection was predictable across water types and flow rates for both UV sources using combined variable modeling, which enabled us to estimate log inactivation of other microorganisms. Following UV disinfection, wastewater quality met the WHO standards for unrestricted irrigation.

United Nations Sustainable Development Goal 6.3 aims to half the proportion of untreated wastewater and increase recycling and safe water reuse. Therefore, developing robust technologies to achieve these goals, specifically in low- to middle-income countries, is of concern. One such technology, gravity-driven woven-fiber microfiltration (WFMF) has been shown to be a reliable, low-cost, and versatile water treatment process. This study investigated a gravity-driven WFMF system for treating secondary wastewater. Given the significant role of the microbial community in biological treatment processes, this investigation focused on the inter-relationship between the microbiomes of the influent, biofilm, and permeate, while further examining the system's performance regarding microbial activity and permeate water quality. The WFMF system reached a quasi-steady state after approximately 10 days. The microbiome analysis, specifically beta diversity analysis, showed that the biofilm and permeate had similar microbiomes, proving a direct impact of the biofilm's microbial community on the permeate water quality. It also showed that the microbial community composition changed within the system. Alpha diversity analysis indicated that biofilm had higher richness and alpha diversity indices (e.g., OTUs and Shannon) than the influent. The system reduced the concentrations of fecal indicators Escherichia coli and Enterococcus spp. and the relative abundance of putative pathogens such as Legionella spp. Furthermore, it reduced microbial activity, as measured by intact cell counts and intracellular ATP, by 48.7% and 58.0%, respectively. Biofilm structure, investigated by various imaging techniques, including scanning electron microscopy (SEM), confocal laser scanning microscopy (CLSM) and optical coherence tomography (OCT), depicted a heterogeneous distribution over the membrane surface. The findings of this study underscore the role of the biofilm on the permeate's microbiome and, consequently, its impact on the permeate's biological stability and suitability for discharge and reuse. Thoroughly understanding microbial dynamics has implications for performance optimization, field implementation, and permeate discharge or reuse.

A decentralized approach to agricultural wastewater reuse could further expand its implementation potential; however, it requires treatment systems that are able to meet the specific economic, operational and treatment needs for that context. This study evaluated gravity-driven woven fiber microfiltration (WFMF), a low cost and robust treatment technology, as pretreatment for ultraviolet disinfection for decentralized agricultural wastewater reuse. Two identical gravity-driven WFMF systems fed with secondary wastewater effluent were operated in parallel. A rapid decline in permeate flux was observed during the first 10 days of operation, reaching stable fluxes of 0.62 and 0.70 L/m2/h. Hydraulic resistance of the mature systems was mostly attributed to fouling reversible by flushing and brushing. OCT images showed that fouling was spread heterogenously on the WFMF surface. The systems were able to significantly reduce turbidity (69.5%), total suspended solids (38.8%), and Escherichia coli (49.4%) while increasing UV transmittance (UVT) at 254 and 280 nm. However, it did not significantly change the concentrations of total or dissolved organic carbon. In the WFMF permeate, turbidity and UVT, regarded as the most impactful parameters for UV disinfection effectiveness, were within the ranges recommended or regulated by the NWRI, USEPA and EU. Overall, the systems improved the quality of the secondary wastewater effluent, properly conditioning it for UV disinfection. Added to the practicality of the gravity-driven operation and the robustness of the woven-fiber microfilters, gravity-driven WFMF systems are a promising pretreatment alternative for UV disinfection for decentralized agricultural wastewater reuse.