Subsurface Wastewater Infiltration Research Articles

The design and operation of subsurface wastewater infiltration systems for domestic wastewater.

Throughout rural regions, large amounts of domestic wastewater are discharged into natural bodies of water without treatment. A well-designed subsurface wastewater infiltration (SWI) system is an effective wastewater pollution removal strategy for small and remote communities due to its low energy consumption, low operational cost, and good performance. This paper describes the types of structures and purification mechanisms of SWI systems, focusing on the design of substrate materials and the optimization of different operation modes including the hydraulic loading rate, pollutant loading rate, intermittent operation, aeration, and shunting distribution. The challenges and trends in the development of SWI systems are also discussed. PRACTITIONER POINTS: The construction and purification mechanisms of SWI system are described. The design of substrates and the optimization of operation modes are focused. The challenges and the development trends for the system are further introduced.

Field study on N2O emission from subsurface wastewater infiltration system under variable loading rates and drying-wetting cycles.

In this field study, the impacts of influent loadings and drying-wetting cycles on N2O emission in a subsurface wastewater infiltration (SWI) system were investigated. N2O emitted under different operation conditions were quantified using static chamber and gas chromatograph techniques. N2O conversion rate decreased from 6.6 ± 0.1% to 2.7 ± 0.1% with an increase in hydraulic loading (HL) from 0.08 to 0.24 m3/m2·d. By contrast, N2O conversion rate increased with increasing pollutant loading (PL) up to 8.2 ± 0.5% (PL 4.2 g N/m2·d) above which conversion rate decreased, confirming that N2O production was under the interaction of nitrification and denitrification. Taking into consideration the pollutants (chemical oxygen demand (COD), NH4+-N, NO3--N and total nitrogen (TN)) removal ratio and N2O emission, optimal loading ranges and drying-wetting modes were suggested as HL 0.08-0.12 m3/m2·d, PL 3.2-3.7 g N/m2·d and 12 h:12 h, respectively. The results revealed that in SWI systems, conversion ratio of influent nitrogen to N2O could be between 4.5% and a maximum of 7.0%.

Comparison of the treatment performance of bio-substrate based and meadow brown soil based subsurface infiltration systems for domestic wastewater treatment

To foster the practical development of subsurface wastewater infiltration (SWI) systems in China, two systems were implemented on the campus of Shenyang University. The bio-substrate filled SWI (BSWI) and meadow brown soil filled SWI (MSWI) system operated under the same operation mode. According to the 12-month experimental results, the bio-substrate had much higher potential to be a good substrate as compared to the meadow brown soil. The maximum adsorbing capability for NH(4)(+)-N of the bio-substrate was 0.724 mg/g, while for the meadow brown soil, the maximum value was 0.471 mg/g. The amounts of nitrifying and denitrifying bacteria of the BSWI were one order of magnitude higher than that for the MSWI. Ammonia, nitrite and nitrate nitrogen concentrations implied nitrification-denitrification process went well in the BSWI. Moreover, the BSWI system maintained efficient pollutants removal, the mean removal efficiencies were 92.3 ± 1.5%, 96.5 ± 3.1%, 90.0 ± 2.1%, 78.6 ± 1.2%, 91.2 ± 1.1% and 99.7 ± 1.0% for COD, BOD(5), NH(4)(+)-N, TN, TP and SS, respectively. As compared with the MSWI system, pollutant removal efficiencies improved by 26.8 ± 2.3% for NH(4)(+)-N, 33.8 ± 1.7% for TN, 22.4 ± 1.4% for COD, 26.0 ± 3.5% for BOD(5) and 14.7 ± 2.9% for TP, respectively.

Feasibility Study of Municipal Wastewater Treatment by a Subsurface Infiltration System in Northeast, China

From October 2009 to September 2010, this study focused on investigation the performance of a subsurface wastewater infiltration (SWI) system in treating domestic sewage, and evaluated the potential of the surface water pollution by using the SWI system. The results showed the removal efficiencies were relatively high: for biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), ammonia nitrogen (NH3-N) and total phosphorus (TP) were 95.0, 89.1, 98.1 87.6 and 98.4%, respectively. Meanwhile, the monitoring of a nearby stream characteristic indicated the SWI system could not decrease the receiving surface water quality.

Performance evaluation of subsurface wastewater infiltration system in treating domestic sewage

This study was to investigate domestic treatment efficiency of a subsurface wastewater infiltration (SWI) system over time. The performances of a young SWI system (in Shenyang University, China, fully operated for one year) and a mature SWI system (in Shenyang Normal University, China, fully operated for seven years) under the same operation mode were contrasted through field-scale experiments for one year. The performance assessment for these systems is based on physical and chemical parameters collected. The removal efficiencies within the young system were relatively high if compared with the mature one: for biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), ammonia nitrogen (NH(3)-N) and total phosphorus (TP) were 95.0, 89.1, 98.1, 87.6 and 98.4%, respectively. However, the removal efficiencies decreased over time. The mean removal efficiencies for the mature SWI system were as follows: BOD (89.6%), COD (87.2%), SS (82.6%), NH(3)-N (69.1%) and TP (74.4%). The results indicate that the mature SWI system successfully removed traditional pollutants such as BOD from domestic wastewater. However, the nutrient reduction efficiencies (including NH(3)-N and TP) decreased after seven years of operation of the mature SWI system. Meanwhile, the SWI system did not decrease the receiving surface water quality.

The use of a subsurface infiltration system in treating campus sewage under variable loading rates

The treatment of domestic sewage from a university campus area with diurnally and seasonally variable loading rates was investigated using a pilot-scale subsurface wastewater infiltration (SWI) system operated from January to August 2010. Operating conditions including hydraulic loading rate (HLR) and pollutant loading rate (PLR) were varied during the operation to investigate their impacts on overall treatment performance. The variation values were 0.040, 0.065, 0.081 and 0.125 m 3/m 2 d for HLR, 6.71, 9.30, 16.80 and 20.00 g BOD/m 2 d for PLR. The results showed that although the influent loading rates were highly variable, including sudden sharp increases in organic matter concentrations, the SWI system performed well throughout its operation. Taking the hydraulic and treatment efficiencies into consideration, HLR of 0.081 m 3/m 2 d and PLR of 16.80 g BOD/m 2 d were recommended. Under this condition, purification processes in the SWI system were gradually established over three weeks, after which the removal efficiencies for chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN) and ammonia nitrogen (NH 3–N) were 87.5 ± 1.6, 91.8 ± 0.7, 80.1 ± 1.1 and 86.9 ± 2.0%, respectively. Overall, eight months of pilot-scale tests indicated the robustness of SWI system in terms of achieving very high quality of treated water under HLR (0.040–0.081 m 3/m 2 d) and PLR (6.71–16.80 g BOD/m 2 d). This study will guide the decision on a full-scale SWI application in the campus area.

Effects of hydraulic loading rate on pollutants removal by a deep subsurface wastewater infiltration system

The subsurface wastewater infiltration (SWI) system proved to be an effective and low-cost technique for decentralized sewage treatment in areas without adequate domestic treatment facilities. Field-scale experiments were conducted through a deep SWI system, with effective depth of 1.5 m, under hydraulic loading rates of 0.040, 0.065, 0.081 and 0.10 m 3/m 2 d. Taking the hydraulic and treatment efficiencies into consideration, the hydraulic loading rate of 0.081 m 3/m 2 d was recommended. Under this condition, NH 3–N, TN, and COD removal efficiencies were 86.2 ± 3.0, 80.7 ± 1.9 and 84.8 ± 2.1%, respectively. In the effluent, NH 3–N concentration declined to 2.3–4.4 mg/L, accounting for 63.2–65.6% of TN. NO 3–N concentration increased from 0.2 to 0.3 mg/L in the influent to 2.0–2.5 mg/L in the effluent. The nitrifying bacteria number declined with increased depth, while the amount of denitrifying bacteria increased. The analysis of results about the nitrifying and denitrifying bacteria distribution indicated that the most effective ranges for nitrification and denitrification process were 0.3–0.7 m and 0.7–1.5 m, respectively.

Soil Clogging During Subsurface Wastewater Infiltration as Affected by Effluent Composition and Loading Rate

AbstractThe soil clogging effects of wastewater effluent composition and loading rate were investigated in pilot‐scale infiltration cells installed in situ in the structured silty clay loam subsoil of a Typic Argiudoll (fine‐silty, mixed, mesic). Over a 70‐month period domestic septic tank effluent (DSTE), graywater septic tank effluent (GSTE) and tapwater (TW) were intermittently applied in an average of 5.2 doses/d to yield daily loading rates of 1.3, 2.6, and 5.2 cm/d. Soil clogging was negligible in all TW treatments and in the GSTE treatments at 1.3 and 2.6 cm/d. In the GSTE treatments at 5.2 cm/d and in all DSTE treatments, severe soil clogging led to continuous ponding of the soil infiltrative surfaces. A logistic model fit to the experimental data confirmed that soil clogging development was highly correlated with the cumulative mass density loadings of total biochemical oxygen demand and suspended solids. After 62 and 70 months of loading, soil properties were determined with depth. Clogged infiltrative surface zones exhibited significant accumulations of organic materials at the infiltrative surface and within the first few millimeters of the soil matrix. This field study demonstrated that higher quality wastewater effluents can be discharged to subsurface infiltration systems at hydraulic loading rates in excess of those utilized for DSTE without stimulating soil clogging development.