On-site treated wastewater disposal systems - The role of stratified filter medias for reducing the risk of pollution

Modeling the fate of viruses in aquifers: Multi-kinetics reactive transport, risk assessment, and governing parameters

The transport of viruses in groundwater is a complex process controlled by both hydrodynamic and reaction parameters. Characterizing the transport of viruses in groundwater is of crucial importance for investigating health risks associated with groundwater consumption from private individual or residential pumping wells. Setback distances between septic systems, which are the source of viruses, and pumping wells must be designed to offer sufficient groundwater travel times to allow the viral load to degrade sufficiently to be acceptable for community health needs. This study consists of developing numerical simulations for the reactive transport of viruses in the subsurface. These simulations are validated using published results of laboratory and field experiments on virus transport in the subsurface and applying previously developed analytical solutions. The numerical model is then exploited to investigate the sensitivity of the fate of viruses in saturated porous media to hydraulic parameters and the coefficients of kinetic reactions. This sensitivity analysis provides valuable insights into the prevailing factors governing health risks caused by contaminated water in private wells in rural residential contexts. The simulations of virus transport are converted into health risk predictions through dose-response relationships. Risk predictions for a wide range of input parameters are compared with the international regulatory health risk target of a maximum of 10-4 infections/person/year and a 30 m setback distance to identify critical subsurface contexts that should be the focus of regulators.

Reduction in pollution load to an urban estuary using a sustainable drainage system treatment train

Rapid urbanisation and industrialisation have placed increased pressure on the ecosystem health of urban estuaries. Sustainable drainage systems (SuDS) are globally accepted practices for managing the water quality of stormwater and effluent discharged into urban systems. The Swartkops Estuary in South Africa is a heavily urbanized estuary that has a long history of pollution, specifically trace metal contamination, originating from industrial sources and urban wastewater. Using a novel SuDS treatment train, the physical characteristics (total suspended solids), macronutrients (orthophosphates, nitrate, ammonium), trace metals (As, Cd, Hg, Fe, Pb, Cu), and E. coli concentrations were measured monthly for one year, both before and after the treatment train. The treatment train consisted of five interconnected 500 L plastic tanks for sedimentation, filtration (sand and stone), biodegradation and floating wetlands. Results indicate that the SuDS treatment train provided an efficient method in reducing the pollution load to this urban estuary, by reducing macronutrient concentrations by 76 %, trace elements concentrations by 74 % and faecal bacteria counts (E. coli) by 80 %.

Microbial niches and dynamics of antibiotic resistance genes in a bio-enhanced granular-activated carbon biofilm treating greywater

Accumulation and transmission of antibiotic resistance genes (ARGs) in greywater treatment systems present risks for its reuse. In this study, a gravity flow self-supplying oxygen (O₂) bio-enhanced granular activated carbon dynamic biofilm reactor (BhGAC-DBfR) was developed to treat greywater. Maximum removal efficiencies were achieved at saturated/unsaturated ratios (R_St/Ust) of 1:1.1 for chemical oxygen demand (97.6 ± 1.5%), linear alkylbenzene sulfonates (LAS) (99.2 ± 0.5%), NH₄⁺-N (99.3 ± 0.7%) and total nitrogen (85.3 ± 3.2%). Microbial communities were significantly different at various R_St/Ust and reactor positions (P < 0.05). The unsaturated zone with low R_St/Ust showed more abundant microorganisms than the saturated zone with high R_St/Ust. The reactor-top community was predominant by aerobic nitrification (Nitrospira) and LAS biodegradation (Pseudomonas, Rhodobacter and Hydrogenophaga) related genera; but reactor-bottom community was predominant by anaerobic denitrification and organics removal related genera (Dechloromonas and Desulfovibrio). Most of the ARGs (e.g., intI-1, sul1, sul2 and korB) were accumulated in the biofilm, which were closely associated with microbial communities at reactor top and stratification. The saturated zone can achieve over 80% removal of the tested ARGs at all operation Phases. Results suggested that BhGAC-DBfR can provide assistance in blocking the environment dissemination of ARGs during greywater treatment.

Reactive-transport modelling of Enterococcus faecalis JH2-2 passage through water saturated sediment columns

The reuse of treated wastewater (e.g. for irrigation) is a common practice to combat water scarcity problems world-wide. However, the potential spread of opportunistic pathogens and fecal contaminants like Enterococci within the subsoil could pose serious health hazards. Additional sources (e.g., leaky sewer systems, livestock farming) aggravate this situation. This study contributes to an understanding of pathogen spread in the environment, using a combined modelling and experimental approach. The impact of quartz sediment and certain wastewater characteristics on the dissemination of Enterococcus faecalis JH2-2 is investigated. The transport processes of advection-dispersion and straining were studied by injecting conservative saline tracer and fluorescent microspheres through sediment packed columns, and evaluating resulting breakthrough curves using models. Similarly, simultaneously occurring reactive processes of microbial attachment, decay, respiration and growth were studied by injecting Enterococcus faecalis JH2-2 suspended in water with or without dissolved oxygen (DO) and nutrients through sediment, and evaluating resulting inlet and outlet concentration curves. The processes of straining, microbial decay and growth, were important when DO was absent. Irreversible attachment was important when DO was present. Sensitivity analysis of each parameter was conducted, and field scale behavior of the processes was predicted, to facilitate future work.

Removal of Pathogens in Onsite Wastewater Treatment Systems: A Review of Design Considerations and Influencing Factors

Conventional onsite wastewater treatment systems (OWTSs) could potentially contribute to the transmission of infectious diseases caused by waterborne pathogenic microorganisms and become an important human health concern, especially in the areas where OWTSs are used as the major wastewater treatment units. Although previous studies suggested the OWTSs could reduce chemical pollutants as well as effectively reducing microbial contaminants from onsite wastewater, the microbiological quality of effluents and the factors potentially affecting the removal are still understudied. Therefore, the design and optimization of pathogen removal performance necessitate a better mechanistic understanding of the hydrological, geochemical, and biological processes controlling the water quality in OWTSs. To fill the knowledge gaps, the sources of pathogens and common pathogenic indicators, along with their major removal mechanisms in OWTSs were discussed. This review evaluated the effectiveness of pathogen removal in state-of-art OWTSs and investigated the contributing factors for efficient pathogen removal (e.g., system configurations, filter materials, environmental and operational conditions), with the aim to guide the future design for optimized treatment performance.

Sand from groundwater treatment coated with iron and manganese used for phosphorus removal from wastewater

This article presents investigations into the removal of PO₄-P from biologically treated wastewater using raw material taken from drinking water treatment filters - quartz sand grains coated with iron and manganese oxide coating (OG). The experiments carried out in laboratory stands used real household wastewater and demonstrated that OG filter media accumulated and removed from wastewater two times more PO₄-P than known reactive filter media Filtralite P. The mean effectiveness of PO₄-P removal from wastewater by filtering at a rate of 2.2 m/h and using OG filter media reached 68%. The pH of the filtrate from OG filter media was stable and reached 7.7 ± 0.2 thus meeting requirements for the discharge of treated wastewater into the natural environment. OG grains are mechanically resistant, do not pollute the filtrate and could therefore be used as filter media for tertiary wastewater treatment.

Viability of a Single-Stage Unsaturated-Saturated Granular Activated Carbon Biofilter for Greywater Treatment

Compared with conventionally collected sewage, source-diverted greywater has a higher potential for on-site treatment and reuse due to its lower contaminant levels and large volume. A new design of granular activated carbon (GAC) biofilters was developed by incorporating unsaturated and saturated zones in a single stage to introduce an efficient, passive, and easy-to-operate technology for greywater on-site treatment at the household scale. The design was customized for its intended application considering various aspects including the reactor’s configuration, packing media, and feeding strategy. With the highest hydraulic and organic loadings of 1.2 m3 m−2 d−1 and 3.5 kg COD m−2 d−1, respectively, and the shortest retention time of 2.4 h, the system maintained an average total chemical oxygen demand removal rate of 94% with almost complete removal of nutrients throughout its 253 days of operation. The system showed a range of reduction efficacy towards five surrogates representing viruses, bacteria, and Cryptosporidium and Giardia (oo)cysts. A well-functioning biofilm was successfully developed, and its mass and activity increased over time with the highest values observed at the top layers. The key microbes within the biofilter were revealed. Feasibility of the proposed technology was investigated, and implications for design and operation were discussed.

Performance of an On-Site Wastewater Treatment System Using Reactive Filter Media and a Sequencing Batch Constructed Wetland

Many on-site wastewater treatment systems, such as soil treatment systems, are not sustainable in terms of purification efficiency, nutrient recycling potential, and economics. In this case study, a sequencing batch constructed wetland (SBCW) was designed and added after a package treatment plant (PTP) using reactive filter media for phosphorus (P) removal and recycling. The treatment performance of the entire system in the start-up phase and its possible applicability in rural areas were investigated. Raw and treated effluents were sampled during a period of 25 weeks and analyzed for nitrogen, phosphorus, BOD7, and bacteria. Field measurements were made of wastewater flow, electrical conductivity, oxygen, and temperature. The entire system removed total-P and total inorganic nitrogen (TIN) by 83% and 22%, respectively. High salt concentration and very low wastewater temperature were possible reasons for these unexpectedly low P and TIN removal efficiencies. In contrast, removal rates of bacteria (Escherichia coli, enterococci) and organic matter (as BOD) were high, due to filtration in the alkaline medium Polonite® (Ecofiltration Nordic AB, Stockholm, Sweden) and the fine sand used as SBCW substrate. High pH in effluent from the PTP was efficiently reduced to below pH 9 in the SBCW, meeting recommendations by environmental authorities in Sweden. We concluded that treating cold on-site wastewater can impair treatment performance and that technical measures are needed to improve SBCW performance.