Wastewater Loading Rate Research Articles

Recycled clay bricks and palm kernel shell as constructed wetland substrate for wastewater treatment: An engineered closed circuit circular economy approach

Wastewater treatment using green technologies contributes significantly to a circular economy. Constructed wetlands (CW) using green substrates or recycled materials are low-cost cleaner technologies that further contribute to a closed circuit. This study assessed the performance of two recycled materials, Waste Clay Brick (WCB) and Palm Kernel Shells (PKS), as suitable substrates in a CW for wastewater treatment. Five (5) horizontal subsurface flow constructed wetlands (HSSF CW), designed and fabricated using galvanized steel, were set up for the treatment of domestic wastewater (sewage). The wetland cells were packed with small (WCBS, PKSS) or large (WCBL or PKSL) particle size substrates with one cell using sand as control. The CW operated under two hydraulic loading rates (HLR), 50l/d (HLR-1) and 80l/d (HLR-2). Overall, the effluent quality of HLR-1 was relatively better than HLR-2. pH and turbidity of effluent were satisfactory and within the Ghana Environmental Protection Agency (EPA) guidelines for discharge of wastewater into surface water bodies. For both hydraulic loading rates, the highest removal efficiencies of BOD5 (73.97%), COD (71.89%), TSS (90.82%), TP (71.13%), TN (49.41%) were recorded for WCB. Coliform removal was highest in the Palm Kernel Shell (98.6%), followed by the control (97.39%). Wastewater treatment efficiency decreased with increasing wastewater loading rates for all parameters in Waste Clay Brick and BOD5 and TP in Palm Kernel Shell. WCB demonstrated superior treatment potential compared to PKS for all parameters except coliform removal.

Nitrogen Attenuation in Septic System Plumes.

The persistence of inorganic nitrogen is assessed in a set of 21 septic system plumes located in Ontario, Canada, that were studied over a 31-year period from 1988 to 2019. In the plume zones underlying the drainfields, site mean NO3 - values averaged 34 ± 27 mg N/L and exceeded the nitrate drinking water limit (DWL) of 10mg N/L at 16 of 21 sites. In plume zones extending up to 30 m downgradient from the drainfields, site mean NO3 - values averaged 24 ± 20 mg N/L and exceeded the DWL at 9 of 13 sites. Site mean total inorganic nitrogen (TIN; NH4 + + NO3 - - N) removal averaged 34 ± 26% in the drainfield zones and 36 ± 44% in the downgradient plume zones, indicating that much of the removal occurred within the drainfields. Removal was much higher at nine sites where drainfield TIN included >10% NH4 + (62 ± 25% removal). TIN removal was not correlated with wastewater loading rate, system age, or sediment carbonate mineral content, but was correlated with water table depth, where shallower water table sites had generally less complete wastewater oxidation. At many of these sites, both NO3 - and NH4 + were present together in the plumes and were lost concomitantly, suggesting that the anammox reaction was making an important contribution to the observed TIN loss. When groundwater nitrate contamination is a concern, considering on-site treatment system designs that lead to a lesser degree of wastewater oxidation, could be a useful approach for enhancing N removal.

Organic Matter Composition of Manure and Its Potential Impact on Plant Growth

Since the advent of flush toilet systems, the aquatic environment has received a massive contaminant flow. Furthermore, the perception of human feces has changed from a useful nutrient source for agriculture to a harmful contaminant. In this study, we compared the nutritional quality of five samples: (1) human manure (HM), (2) human manure from a family mainly eating organic food (HMO), (3) cow manure (CM), (4) poultry manure (PM), and (5) commercial nursery media (CNM). Samples were analyzed in terms of organic and inorganic nutrient contents, molecular composition, seed germination, and chlorophyll concentration. Pyrolysis gas chromatography/mass spectrometry (GC/MS) was used to describe the differences in molecular composition. Three-dimensional excitation and emission matrix fluorescence spectroscopy characterized the organic composition of water extracts. From the results, CNM, PM, and HMO showed humic- and fluvic-like substance peaks, the highest values of potassium and sulfate ions, and of C/N ratios, indicating greater plant growth potential. This was confirmed by their higher chlorophyll concentrations and germination index values. These results contribute knowledge about the positive effects of manure, changing the negative perception of human excreta from waste to resource. This work provides a reference for reducing the wastewater loading rate in society.

Assessing and simulation of membrane technology for modifying starchy wastewater treatment

In this study, a hydrophilic polyethersulfone membrane was used to modify the expensive and low efficient conventional treatment method of wheat starch production that would result in a cleaner starch production process. To achieve a cleaner production, the efficiency of starch production was enhanced and the organic loading rate of wastewater that was discharged into treatment system was decreased, simultaneously. To investigate the membrane performance, the dependency of rejection factor and permeate flux on operative parameters such as temperature, flow rate, concentration, and pH of feed were studied. Response surface methodology (RSM) has been applied to arrange the experimental layout which reduced the number of experiments and also the interactions between the parameters were considered. The maximum achieved rejection factor and permeate flux were 97.5% and 2.42 L min−1 m−2, respectively. Furthermore, a fuzzy inference system was selected to model the non-linear relations between input and output variable which cannot easily explained by physical models. The best agreement between the experimental and predicted data for permeate flux was denoted by correlation coefficient index (R2) of 0.9752 and mean square error (MSE) of 0.0072 where defuzzification operator was center of rotation (centroid). Similarly, the maximum R2 for rejection factor was 0.9711 where the defuzzification operator was mean of maxima (mom).

염료 분해균 증대를 통한 Pilot Plant에서의 담체 내 미생물 생태와 색도처리에 미치는 영향

In a pilot-scale dyeing wastewater treatment using two-type fluidizing media, each thickness of biofilm was 15 and 30 <TEX>${\mu}m$</TEX>, respectively. The numbers of protozoa inhabited in small-size (PEMT A) and big-size (PEMT B) media were <TEX>$7.5{\times}10^4$</TEX> and <TEX>$1.25{\times}10^5$</TEX> cells/ml, respectively, and dominant species were Entosiphon sulcatus var sulcatus in PEMT A and Chlamydomonas reinhardtii in PEMT B, respectively. Flask experiments using the two media revealed that the percentages of color removal were 25.8% in PEMT A and 27.1% in PEMT B after 72-h cultivation, indicating the necessity of bioaugmentation. Experiments for bioaugmentation effect on color removal were carried out in the pilot-scale treatment for 75 d by three-step operation under the control of wastewater loading rate and microbial input rate. Dye degradation occurred mainly in the second reaction tank, and the attachment of augmented dye-degrading microorganisms to media took at least 35 d. Final value of chromaticity in effluent was 227, meeting the required standard. Therefore bioaugmentation onto media was good for color treatment. In summary, thickness of biofilm formed on the media depended upon the size of media, resulting in different ecosystem inside the media. Hence, this affected microbial community and color treatment further. Accordingly, the reduction of operation cost is expected by efficient color-treatment process using bioaugmented media.

Potenciais Impactos de Sistemas Estáticos de Esgotamento Sanitário na Água Subterrânea — Revisão de literatura

This review of literature compiles several studies investigating the potential impacts of on-site sewerage systems on groundwater contamination, mainly by nitrates and pathogens. Some clear connections have been reported in several studies, but the degree and impact of such contamination are poorly understood. The extent of contamination is extremely variable and may be a function of soil conditions, type of treatment system, wastewater loading rates, aquifer characteristics and water level. Consequently, the design, construction and proper maintenance of these systems are crucial to a successful and sustainable operation. Evidence of aquifer contamination seem to be based more on the increasing number of on-site systems worldwide than on the problems actually observed that are directly associated with this type of technology

Fermentative and sulphate-reducing bacteria associated with treatment of an industrial dye effluent in an up-flow anaerobic fixed bed bioreactor

This work aims to study effects of increasing wastewater loading rates (WLRs) on the performance of an up-flow anaerobic fixed bed bioreactor and on the dynamics of the bacterial community of the sludge using polymerase chain reaction–single stranded conformation polymorphism (PCR–SSCP) methods. The analysis showed that WLRs variations influence the bacterial community structure and affect the bioreactor performance. For WLRs of 0.34–0.85gl−1d−1, the bioreactor showed a high performance and maintained highest colour and chemical oxygen demand (COD) removal yields with average values of 95% and 90%, respectively. The molecular fingerprint revealed a positive correlation between the diversity and the bioreactor performance. Increasing the WLR to 1.7gl−1d−1 affected significantly the bioreactor performance, the colour and COD removal efficiencies dropped to average values of 75% and 70%, respectively and bacterial and archaeal communities’ profiles changed.The gas production rates increased when WLR increased. The highest value of 0.68ll−1d−1 was obtained at an hydraulic retention time (HRT) of 1 day. The use of molecular and microbiological methods to recover bacterial populations involved in this anaerobic process showed that fermentative (Clostridium spp.) and sulphate-reducing bacteria (SRB) (Desulfovibrio spp.) were the prominent members of the bioreactor bacterial community.

PENURUNAN BOD DAN COD LIMBAH CAIR INDUSTRI TEKSTIL DI KABUPATEN PEKALONGAN DENGAN METODE MULTI SOIL LAYERING

Multi Soil Layering (MSL) system is a method of wastewater treatment that increase the soils function to purify wastewater. In the construction of MSL, soils mixed with the charcoal and then filled into the box of size 50x14x50 cm in layers structured like brick pattern. The aims of this research are to determine the concentration of BOD and COD on textile industrial wastewater before and after the process by MSL method. It also determines the optimal loading rate of wastewater on the MSL system, and then it can determine the efficiency of MSL system on reducing the concentration of BOD and COD on textile industrial wastewater. The method which used in this research is an experimental method. The wastewater on the MSL system is loaded on the loading rate variety: 160, 320, 480, 640, and 800 L m-2 day-1. The efficiency of MSL system to removing BOD and COD on textile industrial wastewater are determined on optimal loading rate. The research gave result that MSL method could remove BOD and COD on textile industrial wastewater on the optimal loading rate 320 L m-2 day-1. The efficiency of MSL system in removing BOD and COD on textile industrial wastewater are 96.52 and 80.87% respectively. This indicated that the method MSL serve the purpose of effective alternative method in processing of liquid waste textile industry.

A long term assessment of phosphorus treatment by a constructed wetland receiving dairy wastewater

Constructed wetlands are cost effective wastewater treatment systems being increasingly used in agriculture. Efficient phosphorus (P) treatment by wetlands can however, be a challenge due to slow removal mechanisms. As a result, extended contact times are often required to achieve desired treatment. There are also concerns related to the long-term sustaina bility of P treatment. Therefore, a five year dataset from a surface flow constructed wetland located in Bible Hill Nova Scotia, Canada was examined to: 1) determine the effects of continued loading on P treatment and 2) evaluate hydrological impacts on P treatment. The wetland was intensively monitored year-round from November, 2000 through April, 2005 for total P (TP) and soluble reactive P(SRP). Dairy wastewater (milkhouse wash water and liquid manure) was loaded at 1.5 ± 1.0 kg ha−1 d−1 for TP and 1.0 ± 0.9 kg ha−1 d−1 for SRP. Mass reductions for the entire monitoring period were 53.7% and 52.7% for TP and SRP, respectively. Soils in this wetland appeared to have a sustained P adsorption capacity, with treatment being largely influenced by hydrology and fluctuations in wastewater loading rates. Linear regression of monthly TP and SRP mass reductions, with monthly outflow volumes resulted in decreased mass reductions with increased outflow. Monthly mass reductions were > 50% when corresponding outflows were < 100 mm. When monthly outflow exceeded 100 mm, however, mass reductions became highly variable. To maintain effective P management by constructed wetlands, the use of approaches that prevent high external hydrological loadings are recommended.

Bacterial monitoring by molecular tools of a continuous stirred tank reactor treating textile wastewater

This study was performed to examine the effect of the bacterial diversity changes on the performances of a continuously stirred tank reactor (CSTR) treating textile wastewater. The molecular fingerprint established using polymerase chain reaction-single stranded conformation polymorphism (PCR-SSCP) methods showed that bacterial community profiles changed simultaneously with the increase of the wastewater loading rates (WLR). For the two WLR of 0.28gl−1d−1 and 0.37gl−1d−1, the reactor maintained good performances, suggesting that the large bacterial community present a high specific activity. The increase of the WLR from 0.37 to 1.12gl−1d−1 decreased the colour and the chemical oxygen demand (COD) removal efficiencies from 90% to 55% and from 85% to 30%, respectively, explained by the decrease of the bacterial diversity and activity. The changes of the bacterial dominance had no affect on the reactor performances. However, the decrease of the bacterial diversity significantly affected the colour and the COD removal efficiencies. It should conclude that indigo dye-containing textile wastewater treatment required the concerted activity of multiple bacterial populations.

Modeling Trench Sidewall and Bottom Flow in On-Site Wastewater Systems

Little is known about how much wastewater infiltrates the soil via the trench sidewall versus the trench bottom in onsite wastewater systems. Our objectives were to develop a method of simulating trench bottom and sidewall flow using a two-dimensional numerical computer model that would include the trench within the model space and determine how much sidewall flow would occur under steady-state conditions. We used HYDRUS-2D to simulate water flow in a two-dimensional cross section of a conventional gravel-filled trench and the surrounding drainfield. Hydraulic properties of the gravel were assumed (saturated hydraulic conductivity Ks =1,000 cm d−1 ) and simulations were run for drainfield soils consisting of a clay loam ( Ks =3.2 cm d−1 ) and a sand ( Ks =41 cm d−1 ) . Biomats were simulated at the bottom of the trench and part way up the trench sidewall ( Ks =0.2 to 2.8 cm d−1 depending on the simulation). Typical wastewater loading rates for Georgia of 2 and 4 cm d−1 for the clay loam and sand, respecti...

Aerobic decolourization of the indigo dye-containing textile wastewater using continuous combined bioreactors

An aerobic bioprocess was applied to Indigo dye-containing textile wastewater treatment aiming at the colour elimination and biodegradation. A combined aerobic system using continuous stirred tank reactor (CSTR) and fixed film bioreactor (FFB) was continuously operated at constant temperature and fed with the textile wastewater (pH: 7.5 and total chemical oxygen demand (COD): 1185 mg l −1). The CSTR is a 1 l continuous flow stirred tank reactor with a 700 ml working volume, and operated with a variable wastewater loading rate (WLR) from 0.92 to 3.7 g l −1 d −1. The FFB is a 1.5 l continuous flow with three compartments packed with a rippled cylindrical polyethylene support, operated with a variable WLR between 0.09 and 0.73 g l −1 d −1. The combined two bioreactors were inoculated by an acclimated microbial consortium and continuously operated with four total WLR. This system presented high COD elimination and colour removal efficiencies of 97.5% and 97.3%, respectively, obtained with a total hydraulic retention time (HRT) of 4 days and total WLR of 0.29 g l −1 d −1. The effects of WLR on absorption phenomena on the yield of conversion of substrate on biomass ( R TSS/COD) and on the yield of conversion of substrate on active biomass ( R VVS/COD) are discussed. The increase of WLR and the decrease of HRT diminished the performances of this system in terms of decolourization and COD removal explained by the sloughing of biofilm, and the washout phenomena.

Estimating biozone hydraulic conductivity in wastewater soil-infiltration systems using inverse numerical modeling

During operation of an onsite wastewater treatment system, a low-permeability biozone develops at the infiltrative surface (IS) during application of wastewater to soil. Inverse numerical-model simulations were used to estimate the biozone saturated hydraulic conductivity ( K biozone) under variably saturated conditions for 29 wastewater infiltration test cells installed in a sandy loam field soil. Test cells employed two loading rates (4 and 8 cm/day) and 3 IS designs: open chamber, gravel, and synthetic bundles. The ratio of K biozone to the saturated hydraulic conductivity of the natural soil ( K s) was used to quantify the reductions in the IS hydraulic conductivity. A smaller value of K biozone/ K s, reflects a greater reduction in hydraulic conductivity. The IS hydraulic conductivity was reduced by 1–3 orders of magnitude. The reduction in IS hydraulic conductivity was primarily influenced by wastewater loading rate and IS type and not by the K s of the native soil. The higher loading rate yielded greater reductions in IS hydraulic conductivity than the lower loading rate for bundle and gravel cells, but the difference was not statistically significant for chamber cells. Bundle and gravel cells exhibited a greater reduction in IS hydraulic conductivity than chamber cells at the higher loading rates, while the difference between gravel and bundle systems was not statistically significant. At the lower rate, bundle cells exhibited generally lower K biozone/ K s values, but not at a statistically significant level, while gravel and chamber cells were statistically similar. Gravel cells exhibited the greatest variability in measured values, which may complicate design efforts based on K biozone evaluations for these systems. These results suggest that chamber systems may provide for a more robust design, particularly for high or variable wastewater infiltration rates.

Impact of loads, season, and plant species on the performance of a tropical constructed wetland polishing effluent from sugar factory stabilization ponds

The effects of wastewater loading rates and two macrophyte species on treatment of sugar factory stabilization pond effluent were investigated in a pilot-scale free water surface constructed wetland (FWS CW) system in western Kenya. For 12 months, four CWs were operated at a hydraulic loading rate of 75 mm day −1 and four at 225 mm day −1. Half the CWs were planted with Cyperus papyrus and half with Echinochloa pyramidalis. Water samples were taken at the inlets and outlets and analyzed for TP, TDP, NH 4-N, and TSS. Mass removal rates of the selected water quality parameters were compared during three periods designated the short rain (period 1), dry (period 2), and long rain (period 3) seasons. There was a significant linear relationship between the mass removal rate of TP, NH 4-N, and TSS and the mass load, and season had a significant effect on the mass removal rate of TSS, NH 4-N, and TDP. Mass loading rates for TDP were about 78% of those for TP, whereas TDP comprised 78–99% of TP mass outflow rates, indicating a release of dissolved P within the CWs. The only significant difference between the two macrophyte species was associated with mass removal of NH 4-N, with more efficient removal in CWs planted with C. papyrus than those with E. pyramidalis. TP mass removal rates were 50–80% higher when a mean water loss for CWs 6–8 during periods 1 and 2 was assumed to represent evapotranspiration for all CWs in period 3 instead of pan evaporation data. This illustrated the importance of accurate estimations of evapotranspiration for pollutant mass removal rates in CWs in tropical climates.

Temporal changes in hydraulic conductivity of sand porous media biofilters during wastewater infiltration due to biomat formation

Porous media biofilters (PMBs) are commonly used to treat domestic wastewater. Biomats develop at the infiltrative surface of PMBs due to continued wastewater application and create an impedance to flow. The goal of this research is to quantify the temporal evolution of normalized biomat hydraulic conductivity ( K bm/ b bm) and effective hydraulic conductivity ( K e). K e is the overall hydraulic conductivity of the infiltrative zone, including biomat and unsaturated media below the biomat. Research was conducted using eight one-dimensional (1D) sand columns with gravel-free and gravel-laden infiltrative surfaces. The columns were loaded at design rates of 100–200 cm/d for 20 weeks of column operation. The K e values for these continuously loaded columns were determined from analyses of bromide-tracer tests, falling-head permeability tests, and volumetric water content measurements during biomat development. The reduction in the K e due to biomat formation is due to two factors: reduced hydraulic conductivity of the thin biomat, and a reduced hydraulic conductivity of the subsoil due to development of a biomat-induced unsaturated flow regime. Unsaturated hydraulic conductivities of the subsoil below the biomat ( K ss) were estimated from capillary curves and water content measurements. For observed final biomat thicknesses (less than 1 cm), the biomat hydraulic conductivity, K bm, is three orders of magnitude smaller than the unsaturated hydraulic conductivity ( K ss). However, the relatively large thickness of the vadose zone causes the K ss to be an important contributor to the overall K e value. For these columns, the final K e values were approximately two orders of magnitude smaller than the original value. Because the exact thickness of the biomat ( b bm) is unknown during the flow experiments, the hydraulic conductance of the biomat zone is presented using a normalized hydraulic conductivity function ( K bm/ b bm). A similar K bm/ b bm is reached regardless of wastewater loading rate. An exponential relationship exists between the volume of wastewater applied to the column and both K e and K bm/ b bm.

A Study on Organics and Nutrients Removal Mechanisms in Livestock Wastewater Treatment Using EGSB

An advanced way of treating livestock wastewater made use of both Autothermal Thermophilic Aerobic Digestion (ATAD), as a pre-step, and Expanded Granular Sludge Blanket (EGSB), as the post-step. As a result, the chemical oxygen demand (COD) concentration flowing out of the post step, including the EGSB, was 89mg/ℓ, while the suspended solid (SS) concentration was 28mg/ℓ, and the total nitrogen (TN) and total phosphorus (TP) concentrations were 62mg/ℓ and 5.7mg/ℓ, respectively. To maintain a high temperature in the ATAD reactor without external heating, the characteristics of influent were found to be very critical. The temperature of the ATAD reactor was significantly elevated only when the influent TSS was more 50,000mg/ℓ. The EGSB reactor was fed with increasingly higher livestock wastewater loading rates up to 6kg chemical oxygen demand (COD)/ m3/day and an average of 84.7% of the COD and 85.4% of the SS were removed in EGSB. Biogas was generated on the 47th day of operation in the EGSB after startup and its production increased at a rapid rate. The methane percentage within the biogas was initially low but it also increased rapidly, up to 73%. When the HRTs were 0.5-3 days, the COD removal efficiency was over 80%, but did show a increase as the HRT increased to 3 days.

Effect of intermittent aeration regulation of a multi-soil-layering system on domestic wastewater treatment in Thailand

This study investigated the effect of aeration of a multi-soil-layering (MSL) system on domestic wastewater treatment. The MSL system was constructed in a 100×200×150 cm concrete tank. Clayey soil was mixed with sawdust and iron scraps at a ratio of 75:10:15, respectively, based on dry weight. The soil mixture was filled into the tank as blocks, thus forming a brick-like layer pattern. The void spaces between the soil blocks were filled with zeolite. Combined toilet and cafeteria wastewater, which was pre-treated by using settlement tanks, was discharged periodically to the MSL system. The loading rate of wastewater varied from 100 to 600 l m −2 d −1. Aeration was applied to the MSL system at rates of 0, 4000 and 20,000 l m −3 d −1. The results revealed that the aeration assists the removal efficiency of biochemical oxygen demand (BOD 5), chemical oxygen demand (COD) and soluble reactive phosphorus (SRP). When the MSL system was aerated at a rate of 4000 l m −3 d −1 for 1 week, BOD 5, COD and SRP removal efficiencies reached 87.4, 53.2 and 80.3%, respectively. However, at this aeration rate, the efficiency of total nitrogen (TN) removal declined to −26.7%. Aeration at a rate of 20,000 l m −3 d −1 for 3 days was more effective for enhancing BOD 5, COD, TN and SRP removals than aeration at the rate of 4000 l m −3 d −1. The removal percentages of BOD 5, COD, TN and SRP at values of 92.2, 73.3, 15.0 and 74.7, respectively, were recorded. Two months of non-aeration decreased the COD removal efficiency to <27%, whereas the BOD 5, TN and SRP removals were at high levels of 82.1, 65.3 and 83.0%, respectively. This suggested that COD removal needed more intensive aeration than the other parameters. Aeration at a rate of 20,000 l m −3 d −1 alternated with 2 months of non-aeration is appropriate for operating the tested MSL system in Thailand.

多段土壌層法による生物系排水処理 モデル装置の送気位置の違いによる処理能力の比較

The effects of various positions of aeration in Multi-Soil-Layering (MSL) method of bio-genic waste water treatment were investigated. Porous aeration pipes were installed in upper, middle, and lower positions in model MSL systems. Each model MSL packed in 10X50X60cm sized acrylic box. Air was supplied at the rate of 48000 l·m-3·d-1 through the porous pipes installed at various positions. Loading rate of waste water was 288 l·m-2·d-1. In the upper position of aeration, clogging was prevented and nitrogen removal was efficient. But efficiency of aeration was low for high level of removal of COD·BOD and T-P, because air leaked from surface of the system. In the middle position of aeration, the efficiency of T-P removal and decomposition of organic matter were high because of the efficient aeration to create relatively large aerobic parts in the MSL. But nitrogen removal was low. Because of nitrate was leaching. It was thought that anaerobic parts were too small to efficient denitrification. In the lower position of aeration, clogging was happened at the early stages of treatments. Fe(II) and Mn(II) were oxidized efficiently to prevent the solubilization. COD·BOD of final effluent water was also low. Based on this study, if only one aeration position has to be selected, the appropriate aeration position was considered to be the position between the first and second of soil layers of MSL. This aeration position may prevent clogging effectively. Large aerobic condition may contribute to efficient phosphorus and organic matter removals. Nitrogen removal may also be enhanced because of nitrification of the upper position and denitrification of the lower position.However, since each upper, middle, and lower position showed different efficiency characteristics on treatments, the positioning of aeration and the operational condition should be selected depending on the given target of the treatment, including the combinations of the two positions, upper/lower, upper/middle, and middle/lower.

Multicomponent simulation of wastewater-derived nitrogen and carbon in shallow unconfined aquifers: II. Model application to a field site

A multicomponent reactive transport model as presented by MacQuarrie and Sudicky [MacQuarrie, K.T.B., Sudicky, E.A., this volume. Multicomponent simulation of wastewater-derived nitrogen and carbon in shallow unconfined aquifers: I. Model formulation and performance, J. Contam. Hydrol.] is applied to a well-studied wastewater plume in a sandy aquifer near Cambridge, Ontario. Domestic wastewater is released into the unsaturated zone via a drain field at a depth of about 0.8 m. The physical transport parameters for the model are obtained by simulating a non-reactive solute, while kinetic input data for the nitrogen and carbon reaction network are obtained from the literature. The model shows that the wastewater-loading rate has little influence on the moisture content in the unsaturated zone, thus oxygen diffusion in the air phase is an important transport mechanism. The model results are in general agreement with the field-determined moisture and oxygen profiles near the drain field. The simulation results show that oxidation of ammonium and dissolved organic carbon (DOC) goes to completion in the 1.5-m distance between the drain field and the water table, and that calcite dissolution limits the pH reduction to about 0.2 units. The model-predicted nitrate concentrations in the core of the plume are in the range of 20–25 mg N/l and are in good agreement with the field data. Overall, the results for the major reactive species from the model simulation agree well with the geochemical data obtained below the drain field and it is concluded that the major physical and biochemical processes have been correctly captured in the current model formulation.

EVALUATING THE EFFICIENCY OF TOXICITY ABATEMENT IN A CONSTRUCTED WETLAND WITH CERIODAPHNIA DUBIA

Constructed wetlands are becoming increasingly popular as low-cost, high-efficiency means of treating agricultural and municipal wastewaters. Monitoring programs for constructed wetlands usually measure physical and chemical characteristics of wetland treatment, including hydraulic residence time and removal of nutrients (N, P), suspended solids, and biochemical oxygen demand (BOD). However, toxicity abatement is seldom measured as evidence of wetland treatment efficiency. In this study, toxicity tests combined with chemical measurements were employed to measure the efficiency of a constructed wetland in treating swine wastes during fall and winter sampling periods. Although the wetland system operated at three wastewater loading rates, only the high-loading-rate cells were tested because of their year-round flows. Wastewater samples were collected prior to, during, and following wetland treatment to track treatment progress as effluents passed through the wetland cells. Toxicity tests with Ceriodaphnia dubia showed significant toxicity abatement of wastewater as it progressed through the constructed wetland system; however, residual toxicity was still observed in the final wetland effluent. No seasonal differences were observed in toxicity abatement between fall and winter wastewater samples, although nitrate and BOD were removed more efficiently during the fall. Results suggest that, while the constructed wetland system is effective in reducing toxicity in swine wastewater, further pre- or posttreatment or additional dilution is necessary before treated effluents are discharged into surface water.