Performance of novel constructed wetlands for treating solar septic tank effluent.

To improve treatment performance of the solar septic tank technology, novel constructed wetland systems have been proposed as an effective post-treatment system. This study aimed to investigate the treatment performance of the multi-soil layer based constructed wetland (MSL-CW) and comparing with the modified constructed wetland (mCW) for treating solar septic tank effluent in long-term operation. Pilot-scale MSL-CW and mCW units were operated in parallel under the same conditions during the period of 2016-2019. Removal efficiencies of TCOD, SCOD and TBOD in the MSL-CW were not significantly different (p < 0.05) from those of the mCW unit, which were 70-72%, 63-68% and 78-82%, respectively. The removal efficiencies of TSS, TKN, NH4-N and TP were found in the same magnitude in both units. The total coliform and E.coli counts in the effluent of MSL-CW and mCW units were reduced from 105 MPN/100 mL to be lower than 103 MPN/100 mL. These long-term operational results demonstrated that the effluent from the MSL-CW and mCW units could meet the global standards of non-sewered sanitation systems and the WHO guidelines. The effects of seasonal variations and plant harvesting on the monthly treatment performance are discussed in this study.

Comparative study on attached-growth photobioreactors under blue and red lights for treatment of septic tank effluent.

Attached-growth photobioreactors (AG-PBRs) employing low-cost attached-growth media were applied to treat septic tank effluent which contained abundant organic and nutrient matters as well as pathogenic microorganisms. This study investigated effects of blue and red LED lights on organic, nutrient and pathogenic removals, biomass productivity and compositions of microbial community in the AG-PBR system. The experimental results showed the blue AG-PBR to be more effective in removing chemical oxygen demand (COD), total nitrogen (TN) and ammonia nitrogen (NH3-N) and generating biomass productivity than those of the red AG-PBR (P < 0.05). Mass balance analysis indicated that the TN and total phosphorus (TP) were removed mainly by assimilation into the biomass. The TN removal rates via nitrification and denitrification processes in the blue AG-PBR were found to be higher than that of the red AG-PBR, corresponding to the observed results of bacterial biomass and abundances of nitrifying and denitrifying bacterial species in the treatment systems. The maximal areal algal biomass productivity of 47 gDW/(m2. d) in the blue AG-PBRs was found to be higher than those of other algal attached-growth systems. Although, the red and blue AG-PBR systems could effectively treat the septic tank effluent to meet the national and international discharge standards, based on treatment efficiencies and biomass productivity, the blue AG-PBR is recommended for treatment of septic tank effluent.

Temporal variability in domestic point source discharges and their associated impact on receiving waters.

Discharges from the widely distributed small point sources of pollutants such as septic tanks contribute to microbial and nutrient loading of streams and can pose risks to human health and stream ecology, especially during periods of ecological sensitivity. Here we present the first comprehensive data on the compositional variability of septic tank effluents (STE) as a potential source of water pollution during different seasons and the associated links to their influence on stream waters. To determine STE parameters and nutrient variations, the biological and physicochemical properties of effluents sampled quarterly from 12 septic tank systems were investigated with concurrent analyses of upstream and downstream receiving waters. The study revealed that during the warmer dryer months of spring and summer, effluents were similar in composition, as were the colder wetter months of autumn and winter. However, spring/summer effluents differed significantly (P<0.05) from autumn/winter for concentrations of biological oxygen demand (BOD), arsenic, barium (Ba), cobalt, chromium, manganese, strontium (Sr), titanium, tungsten (W) and zinc (Zn). With the exception of BOD, Ba and Sr which were greater in summer and spring, the concentrations of these parameters were greater in winter. Receiving stream waters also showed significant seasonal variation (P≤0.05) in alkalinity, BOD, dissolved organic carbon, sulphate, sulphur, lithium, W, Zn and Escherichiacoli abundance. There was a clear significant influence of STE on downstream waters relative to upstream from the source (P<0.05) for total suspended solids, total particulate P and N, ammonium-N, coliforms and E. coli. The findings of this study found seasonal variation in STE and place effluent discharges as a factor affecting adjacent stream quality and call for appropriate measures to reduce or redirect STE discharges away from water courses.

Oxygen profile and clogging in vertical flow sand filters for on-site wastewater treatment.

13 million people (about 20% of the population) use on-site wastewater treatment in France. Buried vertical sand filters are often built, especially when the soil permeability is not sufficient for septic tank effluent infiltration in undisturbed soil. Clogging is one of the main problems deteriorating the operation of vertical flow filters for wastewater treatment. The extent of clogging is not easily assessed, especially in buried vertical flow sand filters. We suggest examining two possible ways of detecting early clogging: (1) NH4-N/NO3-N outlet concentration ratio, and (2) oxygen measurement within the porous media. Two pilot-scale filters were equipped with probes for oxygen concentration measurements and samples were taken at different depths for pollutant characterization. Influent and effluent grab-samples were taken three times a week. The systems were operated using batch-feeding of septic tank effluent. Qualitative description of oxygen transfer processes under unclogged and clogged conditions is presented. NH4-N outlet concentration appears to be useless for early clogging detection. However, NO3-N outlet concentration and oxygen content allows us to diagnose the early clogging of the system.

Septic tank discharges as multi-pollutant hotspots in catchments.

Small point sources of pollutants such as septic tanks are recognised as significant contributors to streams' pathogen and nutrient loadings, however there is little data in the UK on which to judge the potential risks that septic tank effluents (STEs) pose to water quality and human health. We present the first comprehensive analysis of STE to help assess multi-pollutant characteristics, management-related risk factors and potential tracers that might be used to identify STE sources. Thirty-two septic tank effluents from residential households located in North East of Scotland were sampled along with adjacent stream waters. Biological, physical, chemical and fluorescence characterisation was coupled with information on system age, design, type of tank, tank management and number of users. Biological characterisation revealed that total coliforms and Escherichia coli (E. coli) concentration ranges were: 10(3)-10(8) and 10(3)-10(7)MPN/100 mL, respectively. Physical parameters such as electrical conductivity, turbidity and alkalinity ranged 160-1730 µS/cm, 8-916 NTU and 15-698 mg/L, respectively. Effluent total phosphorus (TP), soluble reactive P (SRP), total nitrogen (TN) and ammonium-N (NH4-N) concentrations ranged 1-32, <1-26, 11-146 and 2-144 mg/L, respectively. Positive correlations were obtained between phosphorus, sodium, potassium, barium, copper and aluminium. Domestic STE may pose pollution risks particularly for NH4-N, dissolved P, SRP, copper, dissolved N, and potassium since enrichment factors were >1651, 213, 176, 63, 14 and 8 times that of stream waters, respectively. Fluorescence characterisation revealed the presence of tryptophan peak in the effluent and downstream waters but not detected upstream from the source. Tank condition, management and number of users had influenced effluent quality that can pose a direct risk to stream waters as multiple points of pollutants.

Removal of nutrients from septic tank effluent with baffle subsurface-flow constructed wetlands.

Three new baffle flow constructed wetlands (CWs), namely the baffle horizontal flow CW (Z1), baffle vertical flow CW (Z2) and baffle hybrid flow CW (Z3), along with one traditional horizontal subsurface flow CW (Z4) were designed to test the removal efficiency of nitrogen (N) and phosphorus (P) from the septic tank effluent under varying hydraulic retention times (HRTs). Results showed that the optimal HRT was two days for maximal removal of N and P from the septic tank effluent among the four CWs. At this HRT, the Z1, Z2, Z3 and Z4 CWs removed, respectively, 49.93, 58.50, 46.01 and 44.44% of TN as well as 87.82, 93.23, 95.97 and 91.30% of TP. Our study further revealed that the Z3 CW was the best design for overall removal of N and P from the septic tank effluent due to its hybrid flow directions with better oxygen supply inside the CW system.

Plantio e desempenho fenológico da taboa (Thypha sp.) utilizada no tratamento de esgoto doméstico em sistema alagado construído / Planting and fenological performance of Thypha sp used in the domestic wastewater treatment under constructed wetland system

Este trabalho teve por objetivo estudar o desempenho da macrófita taboa (Typha sp.) e a remoção de nutriente pela mesma, cultivada em quatro sistemas alagados construídos (SAC), utilizados no tratamento de efluente doméstico, pro-veniente de tanque séptico. Para tanto, foram avaliados órgãos vegetais e quantificadas as seguintes variáveis na água residuária e no tecido vegetal: nitrogênio total (N-Total), fósforo total (P-Total), sódio (Na) e potássio (K). Obtendo-se, como resultado, profundidade média de 27,15 cm, alcançada pelas raízes, bom desenvolvimento da taboa, o que possibilitou a partida do sistema aos quatro meses após o estabelecimento da vegetação e, por meio da remoção da biomassa aérea, contribuição para remoção de 1,69 por cento, 1,64 por cento, 4,94 por cento e 0,74 por cento do aporte de N-Total, P-Total, potássio e sódio, respectivamente.

This study was carried out in under to evaluate the macrophytes (Typha sp) performance and nutrient removal by the same, cropped in four constructed wetlands (SACs), used in treating the domestic wastewater proceeding from septic tank. So, were evaluated vegetable organ and the following variables quantified in either wastewater and vegetable tissue: total nitrogen (N-total), total phosphorus (P-total), sodium (Na) and potassium (K). An average depth of 27.15cm were reached by roots, as well as a satisfactory development of Thypha sp., therefore making possible to beginning the operation of the system at four months after vegetation establishment. The system made possible the following removals of the aerial biomass: 1.69 percent, 1.64 percent, 4.94 percent and 0.74 percent from the contribution of N-total, P-total, potassium and sodium, respectively.