Terms Of COD Research Articles

Selective production of volatile fatty acids at different pH in an anaerobic membrane bioreactor

This study investigated the production of major volatile fatty acid (VFA) components in an anaerobic membrane bioreactor (AnMBR) to treat low-strength synthetic wastewater. No selective inhibition was applied for methane production and solvent-extraction method was used for VFA extraction. The results showed acetic and propionic acid were the predominant VFA components at pH 7.0 and 6.0 with concentrations of 1.444 ± 0.051 and 0.516 ± 0.032 mili-mol/l respectively. At pH 12.0 isobutyric acid was the major VFA component with a highest concentration of 0.712 ± 0.008 mili-mol/l. The highest VFA yield was 48.74 ± 1.5 mg VFA/100 mg CODfeed at pH 7.0. At different pH, AnMBR performance was evaluated in terms of COD, nutrient removal and membrane fouling rate. It was observed that the membrane fouled at a faster rate in both acidic and alkaline pH conditions, the slowest rate in membrane fouling was observed at pH 7.0.

Characterization and removal of antibiotic residues by NFC-doped photocatalytic oxidation from domestic and industrial secondary treated wastewaters in Meric-Ergene Basin and reuse assessment for irrigation

Antibiotics are important contaminants that have become an increasingly big problem due to the discharge of the receiving environment. The presence of these organic based pollutants in influent wastewater can inhibit the biological processes and resist to degradation in wastewater treatment plants. Moreover, the consumption of agricultural products, irrigated with water containing antibiotic residues, leads to major harmful effects to the human body through the food chain. In this study; firstly, a conventional characterization was made in terms of COD, TOC, SS, color and of antibiotic residue characterization of untreated raw (influent) and biologically treated (effluent) water from domestic and industrial wastewater treatment plants located in the Meriç-Ergene Basin. After that, photocatalytic activity test was run under visible light for selected antibiotics (Erythromycin, Ciprofloxacin, Sulphametoxasol) which were detected by HPLC MS/MS in excess amount. Finally, for the photocatalytic oxidation, a new generation NFC (Nitrogen-Floride-Carbon)-doped titanium dioxide photocatalyst, which has never been studied in the literature before, was prepared according to the sol-gel method without using thermal processing. Photocatalysts were characterized by UV–vis DRS reflectance and Laser Raman Spectra measurements. All other analyzes were made according to the standard methods. Considering the conventional characterization results; investigated domestic wastewaters exhibited moderate characteristics while industrial wastewater samples had strong characteristics in terms of COD, TOC and SS pollution in accordance with the literature. By the way, contrary to expectations, antibiotic residue results have proved that the effluent wastewater contains more antibiotics than the influent. This can be explained by the fact that, some antibiotics in domestic wastewaters are probably already trapped in feces and cannot be purified by conventional systems since they are released after biological treatment, as mentioned similar studies in the literature. Moreover, by means of 7 h NFC-doped photocatalytic oxidation under visible light, beside approximately % 62 to %79 COD and 62%–86% TOC removal, %99 to %100 removal of antibiotic residue was provided. According to these results, domestic and industrial secondary treated wastewaters in Meric-Ergene Basin can be advance treated, succesfully, with NFC-doped photocatalyst to remove antibiotic residues besides conventional pollutants. This result show that Meriç-Ergene discharge criteria determined by Forest and Water Ministry of Turkey can be provided with this new type photocatalytic process and healthy reuse of this river for irrigation will be possible.

FBR Technology: Its Potential Application on Reuse of Industrial Wastewater

The treatment performance of the fluidized-bed Fenton process in terms of COD and color removal efficiency on a textile wastewater from a manu­facturing facility in Southern Taiwan was evaluated as a case study for the poten­tial application of fluidized-bed reactor (FBR) technology on reuse of industrial wastewater. Results showed that the effluent COD and color of the textile wastewater met the regulatory requirements of Taiwan when the following con­ditions were used in the treatment: concentration ratio COD:Fe 2+ :H 2 O 2 = 1:0.95:7.94, carrier = 74.07 g/l, initial pH = 3. The COD and color removal effi­ciency of the fluidized-bed Fenton process for synthetic commercial dyeing wastewater and actual textile wastewater were compared. At optimum pH =3, the fluidized-bed Fenton process can remove COD more easily from the commercial dye than from actual textile wastewater. In the case of color removal, the fluid­ized-bed Fenton had high removal efficiency. This study has shown that the fluid­ized-bed Fenton process can not only treat textile waste water to meet Taiwan’s regulatory limits for COD and color but also has the potential to be a technology on reuse of industrial wastewater

Intensification of petroleum elimination in the presence of a surfactant using anodic electrochemical treatment with BDD anode

In this work, the effect of the SDS surfactant during the electrochemical treatment of water-oil effluent, using BDD anode, was studied. Different current densities and surfactant concentrations were evaluated. A satisfactory elimination of organic matter (in terms of COD) was achieved, at higher currents densities (40 and 60mAcm−2) reaching over 94%, regardless of the supporting electrolyte used. Experiments carried out at higher current density (60mAcm−2) in the presence of different amounts of SDS (175, 200, 500 and 1000ppm) achieved promising results to eliminate pollutants from effluent. A favorable degradation of the organic matter was reached in the presence of 500ppm of SDS (over 94% of COD removal). This is an excellent result considering that the initial COD increased 1.7-folds with the addition of SDS, respect to the system in the absence of surfactant. No relevant efficiencies were achieved when the SDS concentration was increased from 500 to 1000ppm, suggesting that there is a critical concentration of SDS in which the positive effect overpass the limit associated to the addition of extra organic matter. A comparison between two supporting electrolytes (Na2SO4 and HClO4) confirmed that sulfate species are released from the SDS, producing electrochemically, persulfate. These species favored the degradation of organic matter, in which a synergic effect with the initial Na2SO4 can be identified. Results clearly indicate that the presence of SDS can be a promising approach for treating organic contaminants of low solubility, such as, in the case of water-oil effluent.

Cost-effective physicochemical treatment of carpet industrial wastewater for reuse

The main objective of this study is to investigate the efficiency of the physicochemical treatment process for removal of hazardous refractory wastewater from carpet industry. Characteristics of carpet industry wastewater in terms of COD, BOD, TSS were 60000, 110, 9800 mg/L. Their complete biodegradation is usually very slow as indicated from the immensely low value of BOD/COD, 0.002.High TSS promote the coagulation/flocculation in which coagulants such as ferric chloride, ferrous sulfate and flocculent are added to wastewater in order to destabilize the colloidal materials, eliminate as much as possible of suspended solids and organic materials. The results showed that ferric chloride (1.2g/l), flocculent (2mg/L) at pH 8 achieved COD removal efficiencies of 97% whereas using ferrous sulfate (1.8 g/l), flocculent (2 mg/L) at pH 7 achieved 98% COD removal. Corresponding TSS removal values were 96 and 97%, respectively. Furthermore, lamellar sedimentation of the treated effluent followed by sand filtration upgrades the finally treated effluent for recycling inside the factory, the residual COD and TSS were70 and5mg/L respectively.The construction cost of the treatment unit (100 m3/d) is about US$ 26000 and the running cost is about US$ 3300/year, providing a saving of about US$ 8064/year.

Ultrasound-induced settleability and membrane filterability of activated sludge treating milk processing wastewater

In practice, established operation of activated sludge treatment system with high biomass concentration is restricted because of difficulty in settling the sludge in clarifiers. Membrane bioreactor is a modified form of activated sludge, and despite the superior advantages, its widespread application is restricted by the membrane fouling. Therefore, in this research, to improve the sludge sedimentation at high biomass concentration in the activated sludge system, high-frequency ultrasound (1.7 MHz) was exerted in clarifier of activated sludge system and its performance was compared with a bioreactor followed by an antifouling ultrafiltration membrane. The antifouling ability of NH2-functionalized multiwall carbon nanotubes (NH2-MWCNTs)-modified nanocomposite UF membrane during filtration of mixed liquor-activated sludge was investigated. Hydraulic retention time (HRT) (8–44 h) and mixed liquor suspended solids (MLSS) (6000–14,000 mg/L) were chosen as the operating variables to analyze the process. The biological process showed high COD removal efficiency throughout the experiments (> 96%). The membrane and high-frequency ultrasound had no effect on the system performance in terms of COD, TKN, TN, TP removal. However, the HRT and MLSS indicated an increasing impact on flux. The effect of ultrasound on the sludge properties, i.e., sludge volume index, sludge settling velocity and height of sludge at high MLSS concentration (14,000 mg/L), was not considerable. It was concluded at MLSS of below 10,000 mg/L, about 40% water recovery was obtained. As a result, activated sludge equipped with ultrasound showed a promising performance; however, its industrial development needs further examinations to attain the design criteria.Graphical

Process performance optimization and mathematical modelling of a SBR-MBBR treatment at low oxygen concentration

Abstract In this study, performances of a SBR-MBBR in terms of COD, TN removal efficiency and sludge production were compared to that of an A/O-MBBR. The SBR-MBBR (40% filling ratio) at 24, 18 and 12 h HRT had a COD and TN removal efficiencies of 88 and 75%, 92 and 72%, 90 and 47%. Increasing the filling ratio to 60% with 12 h HRT, the COD and TN removal efficiencies raised to 93% and 66%, respectively. Thus, increasing the filling ratio of the MBBR the TN removal was improved. The A/O-MBBR configuration achieved a COD and TN removal efficiencies, respectively, of 85% and 72%. This configuration obtained the highest sludge yield due to an increase of the sludge production. Nitrification and denitrification activity tests, performed on attached and suspended biomass, revealed a specialization of the microbial community with the suspended biomass responsible for the denitrification process while the attached biomass for the nitrification. Moreover, a mathematical model consisting of a system of impulsive ordinary differential equations was developed to simulate the SBR-MBBR process. The mathematical model was successfully calibrated and validated through the collected experimental data, resulting in a suitable tool for process efficiency prediction and optimization of operational process conditions.

Prediction of crack tip plasticity induced due to variation in solidification rate of weld pool and its effect on fatigue crack propagation rate (FCPR)

Effect of solidification rate on crack tip plastic zone size at various crack lengths was calculated analytically and numerically by simplified Sih’s and Irwin’s models, respectively. Influence of plastic zone size is explained in terms of COD and elastic stress intensity factor within valid range of small scale yielding approximation. Up to plastic zone size range of 4–5 mm, a good agreement between numerical and analytical plastic zone size and elastic stress intensity factor for all weldments was observed. For high loads and greater crack lengths, experimentally obtained COD values were found 15–19 % more than simulation ones due to rapidly induced plasticity at high crack dimensions. Solidification rate showed a significant influence on FCPR, for solidification rates 13.75 °C/s, 6.97 °C/s and 4.32 °C/s the obtained fatigue strength was 35.29 MPa, 36.26 MPa and 41.32 MPa, respectively.

Hybrid electrochemical-granular activated carbon system for the treatment of greywater

Three-dimensional (3D) flow-through electrochemical reactor filled with granular activated carbon (GAC) was employed for the treatment of greywater. Polarization of GAC by the electric field, without the direct contact with the terminal current feeders, resulted in oxidant production and degradation of the adsorbed/electrosorbed contaminants. This in turn enabled electrochemical regeneration of GAC and an improved performance compared to a conventional two-dimensional (2D) electrochemical system. The synergy between electrooxidation and GAC adsorption enhanced the performance of the 3D system by up to 21% and 23% in terms of COD and TOC removal, respectively, compared to the summed up performances of GAC and 2D electrochemical systems operating separately. In long-term operation of the 3D system with a previously saturated GAC, the regeneration efficiency of GAC was increased from 42 to 65% over 31 consecutive runs. Disinfection efficiency was evaluated using Escherichia coli (E. coli), spores of Clostridium perfringens (SCP) and somatic coliphages (SOMCPH) as model organisms for pathogenic bacteria, protozoan surrogate and viruses, respectively. GAC could not remove any of the abovementioned microbial indicators. 2D and 3D electrochemical systems achieved similar log removals of E. coli (4.6–5.1 log), SCP (0.1–0.6 log) and SOMCPH (3.2–3.3 log). However, the proportions of viable cells from the total cells adsorbed onto the GAC was reduced from 72% to 22% when an electric field was applied, further confirming that electrochemical polarization of GAC caused the killing of the adsorbed microorganisms. Simultaneous adsorption/electrosorption and electrocatalysis in the GAC packed bed lowered the energy consumption from 46 kWh kg COD−1 removed in conventional 2D system, to 30 kWh kg COD−1 removed in the 3D electrochemical system, thus enabling significant savings in the operational costs.

Simulation of Oxidation Ditch with STOAT

This paper examines the use of the modified version of ASM model referred to as IAWQ#2B implemented in STOAT simulation package to model the performance of oxidation ditch process. STOAT is a free simulation package for comprehensive modeling and simulation of long-term treatment plants. The dynamic model was calibrated and validated using real operating data from the wastewater treatment plant. The model was able to produce good match in terms of COD, TN, MLSS concentrations, and effluent TSS without adjustment to any default model parameters apart from the wastewater treatment plant operating parameters, and the influent wastewater characteristics which were determined during the data collection campaign. Additionally, the use of chemical polishing for total phosphorus removal (TP) was reasonably predicted by the model. The model was able to identify ‘on-off aeration operation’ as the reason for ammonia spike at the WWTP.

Benchmark study of photosynthetic bacteria bio-conversion of wastewater: Carbon source range, fundamental kinetics of substrate degradation and cell proliferation

Photosynthetic bacteria (PSB)-bioconversion is a novel method for wastewater treatment and resource recovery. But fundamental knowledge on effective substrate range, cell proliferation and substrate degradation kinetics are lacking. This paper studied the efficient range of carbon source (in terms of COD) and the fundamental kinetics of COD degradation and cell proliferation of this technology. Results showed that the efficient concentration range of carbon source was 500–40,000mg·L−1 COD for PSB, which covers most organic wastewaters. Then the substrate degradation and cell proliferation kinetics were studied using Michaelis-Menten equation and Monod equation. The Vmax, Km, μmax and Ks was 4.80d−1, 7382mg·L−1, 1.23d−1 and 7714mg·L−1 under light-anaerobic condition, and they were 4.27d−1, 4813mg·L−1, 0.59d−1 and 21,295mg·L−1 under dark-aerobic condition; which fell in the range of conventional biological wastewater technologies. This benchmark study lays foundation for further study and scale-up of this novel technology.

BIOREACTOR LANDFILLS: COMPARISON AND KINETICS OF THE DIFFERENT SYSTEMS

The need for more sustainable landfilling has increased interest in bioreactor landfills as a suitable tool for optimising degradation processes. Bioreactors can be categorised as follows: anaerobic, aerobic, semi aerobic and hybrid. The choice of a specific bioreactor can be strongly influenced by the desired treatment objectives (i.e., energy recovery, increased rate of waste stabilisation, washing) as well as by the specific site conditions (e.g., waste characteristics, climate and social/economic situation, regulations). However, the increased rate of waste stabilisation should be the primary driving principle in the bioreactor landfill design (Cossu, 2010). Full-scale bioreactor landfills are still uncommon and one of the reasons is the perception that the effectiveness of this technology is not well demonstrated. This paper aims to contribute to filling this knowledge gap by analysing and comparing the lab scale applications of different types of bioreactors available in the literature and providing a survey of the different methods by considering their respective advantages and disadvantages. Qualitative analysis of the main types of bioreactor landfills is provided according to a few selected characteristics (i.e. energy recovery, biochemical kinetics, technological complexity, costs). Considering landfill sustainability, the discussion is primarily focused on the quantification of the stabilisation capability of the different bioreactors which is calculated in terms of COD and ammonia removal kinetics. The results demonstrate that the optimisation of COD removal kinetics is the highest in aerated bioreactors, while ammonia removal kinetics is maximum in hybrid bioreactors (i.e., 6 and 10 times higher, respectively, compared to the anaerobic bioreactors).

Remediation of Domestic Wastewater Runoff Using Vermi-biofiltration

Remediation of domestic wastewater by indigenous vegetation was carried out using wastewater runoff within Silpakorn University, Sanam Chandra Palace Campus, Thailand. The treatment system utilizes the biological filtration treatment unit working in conjunction with earthworm, the living organism in soil, and vegetation to form a joint wastewater treatment unit, vermi-biofiltration, to treat domestic wastewater. The joint system operates by means of the raw wastewater percolates vertically through layers of physical and biological filtration media in a container tank topped with a layer earthworm-filled soil and vegetation to further phytoremediate the wastewater. The wastewater runoffs were collected from 2 sources having two levels of COD, Low (with COD ranging from 40-100 mg/L) and Medium (with COD ranging from 500-800 mg/L). The subjected wastewater went through 7 cycles of treatment and had their water quality parameters measured to determine the treatment efficiency in comparison to the system with stand-alone filtration. Results showed that the vermi-biofiltration system, combining soil living organism and plant phytoremediation was effective in treating domestic wastewater runoff and yielded significantly better water quality parameters (in terms of COD, TSS, TDS and TS concentration) when compared to system that only undergone filtration.

Preparation of an Aluminum and Iron‐Based Coagulant From Fly Ash for Industrial Wastewater Treatment

Fly ash was investigated to produce a composite coagulant containing aluminum (Al) and iron (Fe) salts through the calcination and leaching processes. The extraction of Al and Fe oxides from fly ash demonstrated similar results for HCl and H2SO4 leaching. Besides, the calcination pretreatment of fly ash (without any additive) was found to be less effective in extraction. However, the conversion efficiencies of Al and Fe were affected greatly by calcination pretreatment with addition of Na2CO3, and leaching conditions of ratio of solution to fly ash (L/S) and H+ concentration. The maximum concentrations of Al and Fe solubilized from fly ash were 0.21 and 0.04 mol/L, respectively, which were attained by calcination pretreatment using an optimal mass ratio (ca. 1:16.7) of Na2CO3 to fly ash at 805°C. These concentrations correspond to conversion efficiencies of 31.2% for Fe and 18.3% for Al in the fly ash. The slurry was filtrated to obtain a solution containing Al‐ and Fe‐sulfates and silicates. The Al/Fe/Si mole ratio indicated the feasibility of further production of inorganic polymer coagulant. The produced coagulant was determined to be effective for treating soybean wastewater and dairy wastewater in terms of COD and SS removal.

Integration of microfiltration and nanofiltration to promote textile effluent reuse

This study investigates the application of a hybrid microfiltration–nanofiltration (MF–NF) process for textile wastewater reclamation. Indigo blue dye was efficiently retained by an MF membrane, allowing its recovery from the concentrated stream. NF technology was successfully applied to polish textile effluent. The NF membrane was evaluated under different transmembrane pressure (8–15 bars), crossflow velocities (0.21–0.84 cm s−1), pH (7–11), and feed temperature (20–40 °C). The best NF performance was provided at a pressure of 12 bar and a crossflow rate of 0.63 cm s−1. The NF performance (in terms of COD, conductivity, colour, and nitrogen removal) was not influenced by pH; however, higher feed pH values resulted in increased membrane fouling. The principal cause of flux decline was due to concentration polarization. Membrane chemical cleaning was sufficient to regain the initial permeability. The NF permeate met the quality requirements for all water demands within the textile industry, while the NF concentrate could be used to wash equipment, print work screens, print paste containers, and floors. The total capital cost (CapEx) of the MF–NF system was estimated at 58,362.50 US dollars and the total operational cost (OpEx) at 0.31 US dollars per cubic metre of effluent.

Characteristics and Mechanism of Biological Nitrogen and Phosphorus Removal Granular Sludge Under Carbon Source Stress

In SBR reactor, the mature granular sludge fed with sodium acetate was gradually cultivated with different carbon sources (sodium acetate/glucose ratio was 1:0, 3:1, 1:1, 1:3 and 0:1, in terms of COD, respectively). During the five stages, the physical, biochemical properties, extracellular polymeric substances (EPS), phosphorus fractions and nitrogen and phosphorus removal efficiency of granular sludge were studied. 705 days' experimental results were showed as follows. At stage Ⅳ, the granular sludge had the smallest diameter of 0.5 mm; moreover the phosphorus release/uptake rate, denitrification rate and the total phosphorus (TP) content were the lowest. While at stages Ⅰ and Ⅱ, the phosphorus release/uptake and denitrification rates were the highest, meanwhile, the TP content reached up to 72.36 mg·g-1, and the EPS content was about 350 mg·g-1, as a result, the nitrogen and phosphorus removal efficiencies were both over 94%. Nevertheless at stage Ⅴ, the biochemical rates were slightly slower than values of stages Ⅰ and Ⅱ, simultaneously the TP, glycogen and EPS contents in sludge were maintained at 69.60 mg·g-1, 224.18 mg·g-1 and 200 mg·g-1, respectively, while high nitrogen and phosphorus removal efficiency was obtained. During all stages, Ca-P was the main phosphorus fraction, and inorganic phosphorus(IP) was closely related to phosphorus removal of granular sludge.

Characterization of residual organic compounds of aerobic degradation of landfill leachate

ABSTRACTThe purpose of this article is to characterize and compare the residual COD of raw landfill leachate and its low and high molecular weight fractions before and after aerobic degradation process. The low and high molecular weight fractions (<10 kDa and >10 kDa, respectively) were obtained by the use of an ultrafiltration cell. Samples of the fractions with molecular weights 10 kDa, as well as the raw leachate, were characterized in terms of COD, protein, carbohydrate and lipid concentration and by biodegradability test. The compound identification of all samples was carried out using gas chromatography coupled with mass spectrometry (GC/MS). The results show that the landfill leachate studied is constituted of approximately 60% of compounds with molecular weight <10 kDa. Approximately 80% of the compounds identified in the leachate had been degraded. This is an indication that most of the compounds that constitute the significant fraction of residual COD correspond to intermediate products and products of condensation of affluent compounds or had been generated during the degradation (SMP). Similar compounds were identified in all effluents of the degradation assay, suggesting the presence of SMP. These compounds, predominantly aliphatic and esters, are characterized by high molecular weight and probable refractory nature.

Remoção biológica de nitrogênio associada à remoção físico-química do fósforo em um reator de lodo ativado operado sob baixa aeração.

No presente trabalho foi avaliado o comportamento de uma unidade piloto de lodos ativados para o tratamento de esgoto sanitário sob a configuração de aeração prolongada de fluxo contínuo, operado com baixa concentração de oxigênio dissolvido no tanque de aeração, a fim de se obter a nitrificação e a desnitrificação simultânea (NDS). Adicionalmente foi avaliado a remoção de fósforo no sistema por meio da dosagem de coagulante (Cloreto Férrico) diretamente no tanque de aeração. Os resultados mostram que a adição do cloreto férrico melhora a qualidade do efluente final em termos de DQO, devido a melhor floculação biológica e como consequência melhor sedimentabilidade do lodo o que pode ser atrativa para processos com NDS. Em relação a remoção de nitrogênio os resultados mostram que é possível de se obter com o processo de NDS um efluente com baixas concentrações de amônia, que foi de 7,0 mgN-NH3-/L e nitrato de 4,0 mg N-NO3-/L. Em relação ao fósforo a dosagem de 170 mgFeCl3/L, apesar de elevada resultou em um efluente com concentrações menores que 1,5 mP/L, apesar da concentração ainda ser alta as dosagens podem ser ajustadas para obtenção de concentrações que atendam os limites recomendados de lançamento.

Two Phase Anaerobic Co Digestion of Tannery Wastewater and Dairy Wastewater: Effect of Operational Parameters on Performance of Hydrolytic–Acidogenic Step

In this study, optimal working conditions for the hydrolytic-acidogenic step in two stageAnaerobic Sequencing Batch Reactor (ASBR) system during anaerobic co digestion of tannery wastewater (TWW) and dairy wastewater (DWW) were investigated. The study was carried out at laboratory scale digesters with 0.4L working volume in semi continuous mode operation under mesophilic temperature (38±2°C). Four mixing ratios of substrates (100:0, 75:25, 50:50, 25:75) at hydraulic retention time (HRT) of 5, 3 and 1days and equivalent organic loading rate (OLR) were examined to assess the effect of each operational parameter on process performance of acidogenic step in the two stageASBR. Based on the result obtained, 50:50 substrate (TWW and DWW) mixing ratio(in terms of COD), 3days HRT and OLR of 3.22gCOD/l/daywere selected as optimum operational conditions for enhanced performance of hydrolytic-acidogenic stage during two stage anaerobic co digestion of the two agro industrial wastes. In addition to this, the degree of acidification was mainly affected by higher OLR and the best result (55.5%) was achieved in the reactor 50:50 operated at 3days HRT and 2.63 gCOD/l/day OLR. In general co digestion of tannery wastewater with dairy wastewater is more important than using tannery wastewater alone for its enhanced performance. This is because of the positive synergistic effects of the co-substrates (dairy wastewater) in terms of well-balanced nutrients, an appropriate C: N ratio and a stable buffering capacity.

Movement of contaminants in the unsaturated zone of the subsurface from a low flush on-site sanitation system in Ivory Park, Johannesburg

This study measured the movement of contaminants in the unsaturated zone of the subsurface from a low-flush on-site sanitation system (also known as an aqua-privy) at three sites in Ivory Park, which at the time that the fieldwork was done was a newly-established informal settlement in Johannesburg. The aim of the study was to provide field data on the movement of contaminants from this sanitation system in a low-income area, in these climatic and subsurface conditions, and to counter a perception that on-site sanitation will inevitably cause pollution. Subsurface conditions consisted nominally of a 1 m thick layer of silty sand with denser gravel at the bottom of it, underlain by a stiff sandy clay (residual granite), with the natural water table more than 15 m below ground surface. In summary, it can be deduced that movement in the unsaturated zone of bacterial indicators, nitrogen and phosphorus from low-flush on-site sanitation systems in lowincome areas is very limited, as long as the effluent remains in the subsurface. More specifically, the impact in terms of COD appears to be negligible, with substantial treatment apparently taking place within the soakaway or within the immediate vicinity thereof. With respect to (i) bacteriological indicators, (ii) nitrogen (in the form of ammonium, nitrite and nitrate) and (iii) phosphorus (in the form of Total Phosphorus), using the distilled water washout technique, there is a very rapid drop-off of contamination with distance from the soakaway. At horizontal distances of 3 m from the soakaway, levels of the measured contaminants had dropped to values consistent with the background levels. The results of this study are not confined to this particular sanitation system. By virtue of the higher hydraulic loading, these results provide an upper bound for contaminant movement from dry on-site systems under similar conditions. Keywords: contaminants, unsaturated zone, subsurface, on-site sanitation