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Decentralized wastewater treatment systems (DWTS) are significant contributors to the eutrophication of surface water bodies due to a lack of treatment mechanisms that target dissolved phosphorus removal. Existing advanced treatment systems are expensive to operate, large in nature, and require frequent maintenance, making them unattractive to DWTS owners. This study aims to investigate the development of a continuous flow treatment system that uses electrocoagulation (EC) to remove dissolved phosphorus from small wastewater streams such as septic tank effluent (STE). Operational parameters, including system hydraulic retention time (HRT), applied current density, and wastewater composition, were optimized to maximize total phosphorus (TP) removal most cost-effectively. Using an HRT of 10 min, an applied current density of 2.0 mA/cm2, and an influent concentration of 20 mg/L, the orthophosphate (OP) and TP removal percentages achieved were 99.9 and 88.1%, respectively. Under these conditions, the average effluent Al3+ concentration in the treated effluent was measured to be 1.0 mg/L while the total suspended solids concentration was measured to be 51 mg/L. The operation cost was estimated to be 0.056 CAD/m3. The results demonstrate that the EC reactor is effective in removing dissolved phosphorus from wastewater and is therefore a viable option in mitigating the risk of downstream eutrophication caused by inadequately treated STE. [ABSTRACT FROM AUTHOR]

The Living Wall (LW) garden system has been employed as a post-treatment system to improve the effluent quality of septic tanks. This improvement primarily involves reducing nutrient levels, as well as facilitating the removal of organic matter and solids in accordance with effluent discharge guidelines. The objective of this study was to investigate the treatment performance of the LW system connected to a septic tank, along with an examination of the microbial communities within the LW units. A laboratory-scale LW system, comprising LW1, LW2, and LW3 units, was employed. The system was fed with effluent obtained from septic tanks and varied by theoretical hydraulic retention time (HRT) of 6, 12, and 24 h. The TCOD, SCOD, TSS, TVS, TKN, and TP removal efficiencies of the LWs were achieved at 62 ± 24, 42 ± 19, 72 ± 21, 66 ± 15, 80 ± 15, and 58 ± 21%, respectively. To classify microbial communities in the soil and gravels collected from each LW unit, the Illumina MiSeq System Sequencer was employed. Nitrospirota was consistently found in all LW units, aiding in the conversion of nitrogen. Fusobacteriota were detected in specific layers of the LW units, indicating varying oxygen levels in the LW system. Highlights: • Living Walls (LWs) effectively eliminate organics, nutrients, and solids to meet the national discharge standard. • Expanding LW units improves nitrogen removal, and microbial communities are crucial for nitrogen removal in LW units. [ABSTRACT FROM AUTHOR]

This paper investigated a combined process of a modified attached-growth anoxic-oxic-anoxic reactor (AG-AOAR) as a sustainable and effective post-treatment system for septic tank effluent was developed. The AG-AOAR was operated by varying hydraulic retention times (HRTs) from 24 to 72 h. The results showed that the AG-AOAR achieved highest removal efficiencies of 84, 66 and 91% of chemical oxygen demand (COD), total nitrogen (TN) and ammonium nitrogen (NH4-N), respectively, under the HRT of 72 h, resulting its effluent meeting the international and national discharge quality standards for non-sewered sanitation system. The Stover-Kincannon model was applicable to describe the kinetic constants of COD, TN, and NH4-N removal in the AG-AOAR (R² > 0.85). Accordingly, the maximum utilization rates (μmax) were determined to be 41.1, 0.15 and 0.50 g/(L-d) for COD, TN and NH4-N removals, respectively, while the saturation constants (KB) were 57.7, 0.12 and 0.51 g/(L-d), respectively. These constant values could be applied for the design of the AG-AOAR to produce treated effluent meeting desired standards. [ABSTRACT FROM AUTHOR]

Vertical Garden Constructed Wetland (VGCW) system has been used as a secondary treatment system to improve effluent quality of septic tanks and cesspools by enhancing nutrients, organic and solid removal according to the guidelines of effluent discharge. This study aimed to investigate the treatment performance of the VGCWs by integrating with diverse plant species and modified media used as secondary treatment for conventional or solar septic tanks. In the study, laboratory-scale VGCW utilizing soil as the media and planted with Water Pennywort were operated at hydraulic retention times (HRT) of 6, 12, and 24 h, while modified planted vertical garden constructed wetlands (mpVGCW) operated at an HRT of 36 h, was fed with effluent collected from a septic tank. The treatment performance of VGCWs treating effluent from the septic tank and operating at an HRT of 24 h was found to achieve the highest removal efficiencies for organic matter, nutrients, and solids (up to over 90%), compared to an HRT of 6 or 12 h. Moreover, the highest log reduction of E.coli of 2.8 was also observed at the 24 h HRT, in comparison to HRTs of 6 or 12 h. The Spider Ivy, Coleus, and Selaginella frosty could be planted in the mpVGCW system to enhance the overall treatment efficiencies with consistently showed high removal efficiencies for TCOD (91.37–93.39%), TKN (97.1–97.8%), and TP (87.18–88.58%). These results suggested the potential of the VGCWs as a secondary treatment system for polishing septic tank effluent and improving environmental quality. • Vertical Garden Constructed Wetlands (VGCWs) operated at a 24-h-HRT exhibited the highest removal efficiencies for TCOD (85%), SCOD (70%), TKN (90%), and TP (80%). • Modified planted vertical garden constructed wetlands (mpVGCWs) efficiently removed the pollutantswith Spider Ivy, Coleus, and Selaginella frosty displaying high removal rates for TCOD (91.37–93.39%), TKN (99.32%), and TP (87.18–88.58%). • Both systems are applicable for treating effluent from communal septic tanks, providing an eco-friendly alternative for environmental protection. [ABSTRACT FROM AUTHOR]