Subsurface Infiltration System Research Articles

Rewetting drained peatlands through subsoil infiltration stabilises redox-dependent soil carbon and nutrient dynamics

Centuries of drainage have stimulated peat decomposition. To counteract the resulting increase in greenhouse gas emission and land subsidence in Dutch agricultural peatlands, passive and active subsurface infiltration (SSI) systems have been developed for peatland rewetting. Here, we studied the effects of SSI systems on groundwater levels, porewater composition and redox potential in four drained peatlands in the Netherlands to determine how soil processes are affected, especially carbon and nutrient dynamics. For three years, groundwater levels were measured continuously, and porewater samples were collected 8–10 times per year in paired SSI (active and passive) and control plots. SSI plots had higher summer groundwater levels and less seasonal fluctuation in groundwater levels than control plots. Redox potential and porewater composition in control plots reflected dominance of oxidation processes during dry periods in the upper soil layers, whereas SSI plots showed dominance of reduction processes in these layers throughout the year. These differences between control and SSI plots were strongest at locations with active SSI systems. Our results show that SSI systems can be effective measures to raise and stabilise groundwater levels in drained peatlands, which results in more stable redox zonation and dominance of anaerobic soil processes, especially during dry periods and when active SSI systems are applied. On the short term, a switch from oxic to anoxic conditions can cause mobilisation of phosphorus and ammonium, while on the longer term the application of SSI can lead to substantial change in carbon and nutrient dynamics. Understanding the full effects of implementing SSI systems and other mitigation measures in drained peatlands is important before they are applied on a large scale.

Experimental investigation and simulation of nitrogen transport in a subsurface infiltration system under saturated and unsaturated conditions

The nitrogen dynamics in a subsurface infiltration system (SIS) are affected by many factors, including temperature, system design, and feed water quality, which are not easily quantified. In this study, a column experiment was conducted to simulate an SIS. The HYDRUS-1D software package was used to investigate and quantify the factors that affect nitrate transport in an SIS. Three treatments were carried out based on different hydraulic conditions, including continuous wetting (CW), wetting/drying (WD), and a specific hydraulic loading rate (SH). The effects of hydraulic conditions and temperature on nitrate transformation were investigated. The model was calibrated and validated using two-year experimental data. Simulations of cumulative outflow volume and nitrate concentration fitted well with the observations. Among the three SISs, the denitrification rate was greatest under unsaturated conditions at high water temperature. The denitrification rate constant had an exponential relationship with temperature. An empirical formula describing this relationship was developed and validated in the SIS. The results showed that the SH column attained the greatest nitrate removal efficiency, mainly due to its low hydraulic loading and long retention time. Overall, the results showed that HYDRUS-1D adequately simulated nitrate transport through the soil column under different temperature and hydraulic conditions in an SIS. The fate of nitrate was directly controlled by the water temperature and hydraulic conditions.

Effect of aeration and hydraulic loading rate on nitrogen removal by subsurface infiltration systems.

This study investigated the effect of hydraulic loading rate (HLR) on matrix dissolved oxygen (DO), organic matter removal, nitrogen removal, N2 O emissions, and the abundances of functional genes participating in nitrogen removal in intermittent aerated mode (IAM) and nonaerated mode (NAM) subsurface infiltration systems (SISs). In contrast to NAM SISs, IAM SISs were able to create aerobic conditions in the upper matrix (above 50cm depth) and anoxic or anaerobic conditions in the lower matrix (below 80cm depth). Subsequently, this enhanced the abundance of functional genes related to nitrogen removal. Chemical oxygen demand (COD) and nitrogen removal performance were significantly higher under IAM SISs than with NAM SISs. Under a HLR of 0.3m3 /(m2 d), the IAM SIS was able to achieve low N2 O emissions (12.6mg/[m2 d]) along with removal efficiencies of 90.5%, 91.4%, and 85.7% for COD, ammonia nitrogen ( -N), and total nitrogen (TN), respectively. PRACTITIONER POINTS: Intermittent aeration successfully realized sequential aerobic and anaerobic conditions at 50 cm depth and at 80 and 110 cm depths of a subsurface infiltration system. Intermittent aeration reduced N2 O emissions and improved hydraulic loading rate and organic matter, nitrogen removal efficiencies. Intermittent aeration enhanced the abundances of amoA, nxrA, napA, narG, nirS, nirK, qnorB, and nosZ.

Fate of nitrogen in subsurface infiltration system for treating secondary effluent

The concentration of total nitrogen (TN) is reported to vary between 20 and 35 mg/L in domestic wastewater. In raw wastewater, ammonia nitrogen (NH4+-N) is the main nitrogen form, accounting for 70%–82% of the TN concentration. Organic nitrogen, nitrite nitrogen (NO2−-N), and nitrate nitrogen (NO3−-N) are present as well. For years, due to the lack of regulatory limits on nitrogen concentration in surface waters, nitrogen from secondary effluent has posed a significant threat to the health of aquatic ecosystems. Researchers have made substantial efforts to reduce the nitrogen concentration in secondary effluent. As a kind of advanced wastewater treatment technology, the subsurface infiltration (SI) system has been widely used, owing to its advantages, which include low operation cost, easy maintenance, and low energy consumption. This review discusses the fate of various forms of nitrogen in SI treatment, including organic nitrogen, NH4+-N, NO2−-N, and NO3−-N. Major biological processes involved in nitrogen removal and the main factors influencing its transformation are suggested. Finally, it is shown that ammonification followed by nitrification-denitrification plays a major role in nitrogen removal. Further research needs to focus on the emission characteristics of gaseous nitrogen (generated from the nitrification, denitrification, and completely autotrophic nitrogen-removal over nitrite (CANON) processes) with respect to their greenhouse effects.

Effects of a New Hydrological Barrier on the Temperatures in the Organic Archaeological Remains at Bryggen in Bergen, Norway

The World Heritage Site of Bryggen in Bergen, Norway, has experienced significant degradation of archaeological deposits as a consequence of changes in the soil water and groundwater balance after urban redevelopment adjacent to the heritage site. Additionally, groundwater temperatures below the heritage site were found to be significantly higher closer to the redeveloped area. One of the main mitigation measures taken to reduce the degradation of the archaeology has been the construction of a hydrological barrier along the sheet piling that divides the redeveloped area and the historic site. A shallow subsurface infiltration system was designed to achieve groundwater levels and flow conditions that are optimal for the preservation of archaeological remains directly along the sheet pile, while reducing drainage and subsidence also further upstream. Monitoring of groundwater level and temperatures after implementation of the hydrological barrier shows that groundwater levels and flow conditions have improved with respect to optimal preservation conditions, and groundwater temperatures have generally been reduced by up to 2 °C.

Pollutants removal in subsurface infiltration systems by shunt distributing wastewater with/without intermittent aeration under different shunt ratios

Matrix dissolved oxygen (DO), removal of COD, TP and nitrogen in subsurface infiltration systems (SISs), named SIS A (without intermittent aeration and shunt distributing wastewater), SIS B (with shunt distributing wastewater) and SIS C (with intermittent aeration and shunt distributing wastewater) were investigated. Aerobic conditions were developed in 50cm depth and anoxic or anaerobic conditions were not changed in 80 and 110cm depth by intermittent aeration. Under appropriate shunt ratios, shunt distributing wastewater improved denitrification and had little influence on COD, TP and NH3-N removal. Under the optimal shunt ratio of 1:2 for SIS C, high average removal rates of COD (90.06%), TP (93.17%), NH3-N (88.20%) and TN (85.79%) were obtained, which were higher than those in SIS A (COD: 82.56%, TP: 92.76%, NH3-N: 71.08%, TN: 49.24%) and SIS B (COD: 81.12%, TP: 92.58%, NH3-N: 69.14%, TN: 58.73%) under the optimal shunt ratio of 1:3.

Effect of hydraulic loading rate on pollutant removal efficiency in subsurface infiltration system under intermittent operation and micro-power aeration

The low hydraulic loading rate (HLR) greatly restricts the wide application of subsurface wastewater infiltration system (SWIS) in densely populated areas. To increase the HLR, an innovative SWIS was developed using cyclic operation mode. In each cycle, a wastewater feeding period is followed by a drying period, in which the aeration is conducted by a medium-pressure fan. Results indicated that the removal rate of TOC and NH4+-N were more than 85% at HLR of 0.5m3/m2d, whereas the TN removal rate was lower than 20%, indicating that the aeration was efficient and denitrification process was largely limited in the SWIS. When HLR decreased from 0.5 to 0.2m3/m2d, the pollutant removal efficiency enhanced slightly except for TN. Overall, the intermittent operation and micro-power aeration, combined with shunting the pollutant loading were really helpful for SWIS to achieve higher HLR, which offers a reference for the design of innovative SWIS.

The Potential of Subsurface Infiltration for the Treatment of Biofil Toilet Technology Effluent

BTT effluent and sampled at ports spaced at 0.3 m, 0.8 m, and 1.5 m depths. Using the samples, parameters like COD, BOD5, TSS, T-N, NO3-N, NO2-N, PO4-P, and pathogenic indicator microbes were monitored. RLS and SS columns efficiently removed COD, BOD5, and TSS from the BTT effluent below the Ghana Environmental Protection Agency (GH EPA) guideline values. Up to 99% COD removal were observed in RLS column. A two to five log pathogen removal was recorded for the soil columns. The RLS and SS were found to have a high efficacy for contaminant removal with up to 80% of all contaminants being removed at a depth of 0.3 m along the soil columns. Thus the subsurface infiltration system can serve as a promising technology for the BTT effluent treatment. The study recommends the incorporation of infiltration systems to the BTT especially for areas with high water table or clayey soils.

Correlations of Substrate Microorganisms and Enzyme Activities with Wastewater Purification Effects in Subsurface Infiltration System

The number of substrate microorganisms and enzyme activities of a lab-scale subsurface infiltration system (SIS) were monitored by plate counts, MPN and colorimetric analysis. The removal rates of BOD, COD, TP, TN and ammonia-N were measured. The results showed there were significantly positive correlation (P<0.05) between numbers of bacteria, fungi in the substrate and removal rates of COD and BOD. The correlation between number of nitrifying bacteria and removal rates of ammonia-N and correlation between number of denitrifying bacteria and removal rates of TN were significant. Meanwhile, a significant correlation between phosphatase activities and removal rates of TP (r=0.9885, P<0.05) can be also found. There was significantly positive correlation between urease activities and removal rates of TN (r=0.9698, P<0.05). These conclusions give reference to future research on utilizing substrate microorganisms and enzyme activities as an evaluating wastewater purification effects in SIS.

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.

Nutrient Release from Disturbance of Infiltration System Soils during Construction

Subsurface infiltration and surface bioretention systems composed of engineered and/or native soils are preferred tools for stormwater management. However, the disturbance of native soils, especially during the process of adding amendments to improve infiltration rates and pollutant removal, may result in releases of nutrients in the early life of these systems. This project investigated the nutrient release from two soils, one disturbed and one undisturbed. The disturbed soil was collected intact, but had to be air-dried, and the columns repacked when soil shrinkage caused bypassing of water along the walls of the column. The undisturbed soil was collected and used intact, with no repacking. The disturbed soil showed elevated releases of nitrogen and phosphorus compared to the undisturbed soil for approximately 0.4 and 0.8 m of runoff loading, respectively. For the undisturbed soil, the nitrogen release was delayed, indicating that the soil disturbance accelerated the release of nitrogen into a very short time period. Leaving the soil undisturbed resulted in lower but still elevated effluent nitrogen concentrations over a longer period of time. For phosphorus, these results confirm prior research which demonstrated that the soil, if shown to be phosphorus-deficient during fertility testing, can remove phosphorus from runoff even when disturbed.

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.

Study on nitrogen removal enhanced by shunt distributing wastewater in a constructed subsurface infiltration system under intermittent operation mode

Subsurface wastewater infiltration system is an efficient and economic technology in treating small scattered sewage. The removal rates are generally satisfactory in terms of COD, BOD 5, TP and SS removal; while nitrogen removal is deficient in most of the present operating SWIS due to the different requirements for the presence of oxygen for nitrification and denitrification processes. To study the enhanced nitrogen removal technologies, two pilot subsurface wastewater infiltration systems were constructed in a village in Shenyang, China. The filled matrix was a mixture of 5% activated sludge, 65% brown soil and 30% coal slag in volume ratio for both systems. Intermittent operation mode was applied in to supply sufficient oxygen to accomplish the nitrification; meanwhile sewage was supplemented as the carbon source to the lower part in to denitrify. The constructed subsurface wastewater infiltration systems worked successfully under wetting-drying ratio of 1:1 with hydraulic loading of 0.081 m 3/(m 2 d) for over 4 months. Carbon source was supplemented with shunt ratio of 1:1 and shunt position at the depth of 0.5 m. The experimental results showed that intermittent operation mode and carbon source supplementation could significantly enhance the nitrogen removal efficiency with little influence on COD and TP removal. The average removal efficiencies for NH 3-N and TN were 87.7 ± 1.4 and 70.1 ± 1.0%, increased by 12.5 ± 1.0 and 8.6 ± 0.7%, respectively.

Nitrogen transformation in two subsurface infiltration systems at pilot scale

Nitrogen removal and transformations were studied in two pilot-scale combinations of a special configuration of a subsurface wastewater infiltration system with vertical flow named symbiotic treatment ®. Both pilot-scale combinations operated in parallel and each one consists of four stages in series, one of them with a vertical distribution of stages and the other one with a horizontal distribution. The main differences between them were the separation between stages (presence (the horizontal distribution)/absence (the vertical distribution) of filtration between steps), the hydraulic load (0.113 m 3/m 2 h and 0.082 m 3/m 2 h for the horizontal and the vertical distribution, respectively) and the depth of the soil filters (1 m each stage in the horizontal distribution whereas the depths in the vertical distribution ranges from 20 cm to 40 cm). Results of both configurations showed elevated dissolved oxygen concentration, and high removal of organic matter and total suspended solids (with mean removal values of 96% for COD for both plants and 90% and 98% for TSS for the vertical and the horizontal distribution, respectively). High total Kjeldahl nitrogen removals were obtained in both configurations (mean removals of 70% and 90% for the vertical and the horizontal distribution, respectively). Whereas the nitrification potential was higher in the configuration with horizontal distribution which includes pumping and filtering between stages and higher depth of the soil filters, both tested configurations showed promise for nitrification of wastewater, ammonia nitrogen was efficiently transformed to nitrate.

Nitrogen removal enhanced by shunt distributing wastewater in a subsurface wastewater infiltration system

Three pilot subsurface wastewater infiltration systems filled with the same mixed matrix made of 80% brown soil and cinder at a weight of 20% were constructed in the laboratory. All systems worked successfully in the intermittent feeding mode with total hydraulic loading of 4 m 3/(m 2 d) for over 2 months, with the optimal parameters of shunt ratio of 1:1 and shunt position at the depth of 0.7 m was achieved on the basis of large amounts of experimental data. The experiment results showed that shunt distributing wastewater could significantly improve the nitrogen removal in the subsurface infiltration system and the average removal rates of TN and NH 4-N increased by 10% and 5.67%, respectively. Shunt distributing wastewater had little influence on the removal rates of COD and TP. The results suggested that shunt distributing wastewater was simple and effective for nitrogen removal.

Seasonal Performance Variations for Storm-Water Management Systems in Cold Climate Conditions

Lack of widespread adoption of low-impact development LID designs in northern climates is in large part due to concerns about poor winter performance relating to 1 frozen filter media; and 2 dormant biological functions. An examination of six varied LID designs, in contrast with conventional best-management practices BMPs and manufactured systems illustrated that seasonal functionality was evident for many systems; however, the LID designs were consistently top storm water management performers. The designs were tested and monitored for cold climate performance from 2004-2006 to assess: filter media frost penetration, hydraulic efficiency, and seasonal variations of contaminant removal efficiency. LID systems evaluated included: two types of bioretention systems, a surface sand filter, a subsurface gravel wetland, a street tree, and porous asphalt. The LID performance data were contrasted with conventional structural BMPs swales, retention pond and some select manufactured storm-water systems hydrodynamic separators; 3 a filtration system, and a subsurface infiltration system. Seasonal performance evaluations indicate that LID filtration designs differ minimally from summer to winter, while smaller systems dependent largely on particle settling time demonstrated a marked winter performance decline.

Pollution of soil and groundwater from infiltration of highly contaminated stormwater - a case study

A surface and a sub-surface infiltration system that received runoff water from trafficked roads for several decades was dug up and the contamination with heavy metals, PAH and AOX was investigated. Most measured solid phase concentrations exceeded background concentrations in nearby surface soils and sub-surface sediments and some even exceeded guidelines fixed to preserve the fertility of soil. However, the contamination decreased rapidly with depth. None of the measured metal concentrations in simulated soil solutions exceeded defined drinking water quality standards. Surprisingly, the surface and the sub-surface infiltration system seemed to be equally good at retaining pollution. This indicates that the runoff sludge found in such infiltration systems plays an important role both as a source and a sorbent for stormwater contaminants. The study does not point at a considerable risk for groundwater contamination due to stormwater infiltration, but highlights that well absorbable contaminants readily available in urban stormwater runoff eventually build up in surface soils and sub-surface sediments to environmentally critical concentration levels. Thus, on the one hand stormwater infiltration systems may act as effective pollution traps and on the other, they may pose a potential solid waste disposal problem that future stormwater management based on local infiltration will have to face.

Pollution of soil and groundwater from infiltration of highly contaminated stormwater – A case study

A surface and a sub-surface infiltration system that received runoff water from trafficked roads for several decades was dug up and the contamination with heavy metals, PAH and AOX was investigated. Most measured solid phase concentrations exceeded background concentrations in nearby surface soils and subsurface sediments and some even exceeded guidelines fixed to preserve the fertility of soil. However, the contamination decreased rapidly with depth. None of the measured metal concentrations in simulated soil solutions exceeded defined drinking water quality standards. Surprisingly, the surface and the sub-surface infiltration system seemed to be equally good at retaining pollution. This indicates that the runoff sludge found in such infiltration systems plays an important role both as a source and a sorbent for stormwater contaminants. The study does not point at a considerable risk for groundwater contamination due to stormwater infiltration, but highlights that well absorbable contaminants readily available in urban stormwater runoff eventually build up in surface soils and sub-surface sediments to environmentally critical concentration levels. Thus, on the one hand stormwater infiltration systems may act as effective pollution traps and on the other, they may pose a potential solid waste disposal problem that future stormwater management based on local infiltration will have to face.

Experimental assessment of soil and groundwater contamination from two old infiltration systems for road run-off in Switzerland

Surface and sub-surface infiltration systems for road run-off at two sites in Switzerland were investigated by sampling and analysing the run-off sludge and soil found in the systems. The infiltration systems were between 12 and 45 years old. Measured pollutant parameters included the heavy metals Cr, Co, Ni, Cu, Zn, Cd and Pb, a number of polycyclic aromatic hydrocarbons (PAH) and adsorbed organically bound halogens (AOX). Total concentrations were measured to assess the extent of soil contamination. Further, metal concentrations were measured in equilibrated aqueous extracts to simulate naturally occurring concentrations in percolating water. In the infiltration systems the pollutant concentrations decreased rapidly to background levels within depths less than 1.5 m. The potential for groundwater contamination from infiltration of road run-off appears to be limited, but soil and run-off sludge found in infiltration systems can be heavily contaminated. Noteworthy, the run-off sludge itself plays an important role as pollutant source and sorbent.