Effluent Suspended Solids Research Articles

Evaluation of three turbulence models in predicting the steady state hydrodynamics of a secondary sedimentation tank

The secondary sedimentation tank (SST) is a sensitive and complicated process in an activated sludge process. Due to the importance of its performance, computational fluid dynamics (CFD) methods have been employed to study the underflow hydrodynamics and solids distribution. Unlike most of the previous numerical studies, in the present investigation, the performance of three different types of turbulence models, standard k-ε, RNG k-ε and Realizable k-ε, are evaluated. Firstly, two-dimensional axisymmetric CFD models of two circular SSTs are validated with the field observations. Next, comprehensive comparisons are presented of the model predictions of the key physical quantities, such as the concentration of effluent suspended solids (ESS), and returned activated sludge (RAS), sludge blanket height (SBH), turbulent properties and flow and concentration patterns.A surprising result shows that the prediction of the ESS concentration is not sensitive to the change of turbulence models; while remarkable prediction difference can be observed in the inlet zone and near-field of sludge hopper and SBH. The results suggest that more observations inside the inlet zone are needed to achieve better model calibration and correct application of the turbulence model, which can be crucial to optimizing the geometry of inlet structure and sludge hopper as well as changing return solids concentration for the operation.

CASE STUDY ON NITRIFICATION RATES IN A NON-STIRRED MEMBRANE-AERATED BIOFILM REACTOR OPERATED UNDER LAMINAR REGIME

A lab-scale non-stirred membrane-aerated biofilm reactor with a volume of 14.2 L was operated under laminar flow regime with inorganic synthetic wastewater to assess tertiary nitrification rates. Nitrifying counter-diffusive biofilm grown over microporous polypropylene tubular membranes supplied with atmospheric air at low pressure (3.45 kPa). The reactor was operated at very low water-velocities (in cm/s): from 2.3×10-4 to 2.3 × 10-3. In all runs, the influent ammonium concentration was kept constant ( 26 mg-N/L). By changing the volumetric inflow, the membrane-aerated biofilm (MAB) was tested at seven different ammonium applied loads (range: 0.57 - 6.04 g-N/m2 d). The corresponding ammonium removal rates ranged 0.56 to 3.02 g-N/(m2 d). The percentage of biological ammonium removal presented a range from 50% to 98%. As expected, due to passive experimental dynamic conditions to achieve an ammonium removal percentage greater than 80% a hydraulic retention time of 19 h was required. Clean membrane oxygen transfer rate was evaluated. The nitrifying MAB was found to enhance the oxygen transfer across the membrane when the surface nitrification rates were high. A significant drop in electrical conductivity that is proportional to the ammonium removed was observed. Thus, conductivity measurement can be used as a simple control method of ammonium removal extent. Effluent suspended solids were not detected, therefore a sedimentation process was unnecessary.

CASE STUDY ON NITRIFICATION RATES IN A NON-STIRRED MEMBRANE-AERATED BIOFILM REACTOR OPERATED UNDER LAMINAR REGIME

A lab-scale non-stirred membrane-aerated biofilm reactor with a volume of 14.2 L was operated under laminar flow regime with inorganic synthetic wastewater to assess tertiary nitrification rates. Nitrifying counter-diffusive biofilm grown over microporous polypropylene tubular membranes supplied with atmospheric air at low pressure (3.45 kPa). The reactor was operated at very low water-velocities (in cm/s): from 2.3×10-4 to 2.3 × 10-3. In all runs, the influent ammonium concentration was kept constant ( 26 mg-N/L). By changing the volumetric inflow, the membrane-aerated biofilm (MAB) was tested at seven different ammonium applied loads (range: 0.57 - 6.04 g-N/m2 d). The corresponding ammonium removal rates ranged 0.56 to 3.02 g-N/(m2 d). The percentage of biological ammonium removal presented a range from 50% to 98%. As expected, due to passive experimental dynamic conditions to achieve an ammonium removal percentage greater than 80% a hydraulic retention time of 19 h was required. Clean membrane oxygen transfer rate was evaluated. The nitrifying MAB was found to enhance the oxygen transfer across the membrane when the surface nitrification rates were high. A significant drop in electrical conductivity that is proportional to the ammonium removed was observed. Thus, conductivity measurement can be used as a simple control method of ammonium removal extent. Effluent suspended solids were not detected, therefore a sedimentation process was unnecessary.

Dynamic Simulation of Petrochemical Wastewater Treatment Using Wastewater Plant Simulation Software

A dynamic simulation model was developed, calibrated and validated for a petrochemical plant in Terengganu, Malaysia. Calibration and validation of the model was conducted based on plant monitoring data spanning 3 years resulting in a model accuracy (RMSD) for effluent chemical oxygen demand (COD), ammoniacal nitrogen (NH3-N) and total suspended solids (TSS) of ±11.7 mg/L, ±0.52 mg/L and ± 3.27 mg/L respectively. The simulation model has since been used for troubleshooting during plant upsets, planning of plant turnarounds and developing upgrade options. A case study is presented where the simulation model was used to assist in troubleshooting and rectification of a plant upset where ingress of a surfactant compound resulted in high effluent TSS and COD. The model was successfully used in the incident troubleshooting activities and provided critical insights that assisted the plant operators to quickly respond and bring back the system to normal, stable condition.

Design of Aeration Tank and Clarifier. A Discussion.

When the designer faces the need to calculate the size of the parts, usually reinforced concrete or metal sheet tanks, and the operating variables that occur in an AS WWTP, he becomes aware that there are not enough preliminary data to solve the formulas to be applied. In the classical formula to look for mixed liquor volatile suspended solids, MLVSS = Xv, produced in the aeration tank: Xv = (SRT*Y*(BODi – BODesc)) / (HRT*(1 SRT*kd)). Biochemical oxygen demand in a five day test of raw wastewater, BODi, is known by analyzing it. BODesc, the five day test of BOD that escaped treatment is easily defined from required effluent suspended solids, SSef. Site parameters: kinetic coefficient of yield, Y, and kinetic coefficient of decay, kd, should be provided by a certified laboratory. There are still 3 unknown variables that are: hydraulic retention time, HRT; solids retention time, SRT; and mixed liquor volatile suspended solids, MLVSS or Xv. When addressing the aeration tank, called reactor, the designer supposes two of these variables to find the third and then test it to see if it complies with accepted practice. If not then he tries again until he finds a satisfactory result. This paper proposes the application of MS Excel, simply Excel, for finding the amount of Xv produced in the reactor for all possible values of HRT and SRT for the type of AS WWTP considered. The respective range of these variables, with which successful AS plants operate in the U. S. A., is presented as Table 1 that is part of Table 8-16 of Reference 4. Then the designer assigns an area, A, for the secondary settler, called clarifier, and applies State Point theory to the solids gravity flux graph, called Graph. Then he draws lines that represent weir overflow, minimum and maximum underflows. Then he chooses a compromise between initial and operating costs and flexibility of the WWTP.

Effects of high-concentration influent suspended solids on aerobic granulation in pilot-scale sequencing batch reactors treating real domestic wastewater

The aim of this study was to investigate the effect of high-influent-concentration suspended solids (SS) on the cultivation, structure and long-term stability of aerobic granular sludge (AGS). Cultivation and long-term stability of AGS were monitored in two pilot-scale sequencing batch reactors fed with raw (R1) and settled (R2) domestic wastewater, representing high and medium SS content, respectively. The real domestic wastewater had high chemical oxygen demand (COD) content (1100 ± 270 mg COD L−1). Aerobic granular sludge was cultivated in 44 days (R1) and 25 days (R2) under the conditions of high settling velocity (18 m h−1) and high organic loading rate (OLR) (2.1–2.4 kg COD m3 day). The AGS in both reactors had similar structural properties during long-term operation and remained structurally and functionally stable during the last five months of operation. Comparative evaluation of the results indicated that the high influent SS content of the real domestic wastewater had a positive influence on maintaining significantly lower SVI30 and relatively lower effluent SS concentration. Moreover, a higher influent SS content resulted in smaller mature granules during the stable period. Microbial community analyses helped to understand the aerobic granular sludge structure and showed that the sludge retention time and OLR affected the granular sludge population. The high influent SS increased biomass detachment from the granular sludge surface and caused wash-out of some bacteria colonizing the exterior of the granular sludge.

Effect of Hydraulic Retention Time on the Performance of High-Rate Activated Sludge System: a Pilot-Scale Study

Conventional activated sludge (CAS) technology has been the most commonly applied technology for treatment of municipal wastewater for more than a century; however, a significant portion of energy content of the wastewater cannot be recovered by this technology. Therefore, different modifications can be applied to the CAS technology in order to increase the energy harvesting from wastewaters. In this paper, physically treated wastewater from a municipal preliminary wastewater treatment plant (WWTP) was treated at a pilot-scale high-rate activated sludge (HRAS) system. The HRAS system was operated under three different hydraulic retention times (HRTs) and the treatment performances were evaluated. Within this concept, HRTs of 130, 95, and 60 min were tested. The results revealed that total chemical oxygen demand (tCOD) removal of 59% was achievable and the effluent total suspended solids (TSS) concentration was 90 mg/L at the HRT of 60 min. Effluent COD and TSS concentrations decreased with the decrease in HRT by means of enhanced flocculation and sedimentation. This is confirmed by the improvement of sludge volume index (SVI) values at decreased HRTs. The calculated mass balance showed that more COD was diverted to sludge stream with decrease in HRT. Diversion of more COD to sludge can improve the energy balance of wastewater treatment by the application of anaerobic sludge digestion. By this way, HRAS process would be a promising technology in the concept of energy efficient wastewater treatment systems.

Sludge Reduction in the Activated Sludge Process Strengthened by Enhanced Ozonation Oxidation.

A novel radial-axial mixer and microbubble ozone reactor for enhancing sludge disintegration was designed. In the batch studies, the new reactor was shown to be significantly effective in improving sludge disintegration and increasing ozone utilization. For ozone dosages of 0.02 to 0.3 gO3/gTSS (total suspended solids) at pH = 10, the average sludge disintegration ratio was more than 17 ± 0.83% higher than that of the conventional reactor. An activated sludge process coupled with discharged sludge ozonated was run for 60 days to evaluate the influence of ozonated sludge feeding on the sludge yield coefficient and effluent quality. Although the effluent chemical oxygen demand (COD) and suspended solids (SS) increased slightly, these values were well below the discharge limit. Furthermore, a sludge reduction efficiency of 95% was attained. The experimental results indicated that the combination of sludge ozonation with the activated sludge process could generate a high quality of effluent and a small sludge yield.

Soluble microbial products (SMPs) in a sequencing batch reactor with novel cake filtration system

The formation, composition and characteristics of soluble microbial products (SMPs) were investigated in a novel system which coupled a sequencing batch reactor with a cake filtration system. Both suspended solids (SS) and turbidity were significantly removed, resulting in effluent SS of 0.12 mg L−1 and turbidity of 0.72 NTU after cake filtration. The average concentrations of proteins and carbohydrates decreased respectively from 4.0 ± 0.4 and 7.1 ± 0.6 mg/L in the sequencing batch reactor (SBR) mixed liquor, to 0.85 ± 0.21 and 1.39 ± 0.29 mg/L in the cake filtration effluent. Analysis of the molecular weight (MW) distribution of SMPs revealed a substantial reduction in the intensity of high-MW peaks (503 and 22.71 kDa) after cake filtration, which implied the sludge cake layer and the underlying gel layer may play a role in the effectiveness of cake filtration beyond the physical phenomenon. Three-dimensional excitation emission matrix fluorescence spectroscopy indicated that polycarboxylate- and polyaromatic humic acids were the dominant compounds and a noticeable decrease in the fraction of these compounds was observed in the cake filtration effluent. Analysis with GC-MS set for detecting low-MW SMPs identified aromatics, alcohols, alkanes and esters as the dominant compounds. SMPs exhibited both biodegradable and recalcitrant characteristics. More SMPs (total number of 91) were accumulated during the SBR start-up stage. A noticeable increase in the aromatic fractions was seen in the SBR effluent accoutring for 39% of total compounds, compared to the SBR mixed liquor (28%). Fewer compounds (total number of 66) were identified in cake filtration effluent compared to the SBR effluent (total number of 75).

Characterisation of water quality in effluents of land-based abalone farms in the Western Cape, South Africa

AEI Aquaculture Environment Interactions Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections AEI 9:87-102 (2017) - DOI: https://doi.org/10.3354/aei00217 Characterisation of water quality in effluents of land-based abalone farms in the Western Cape, South Africa T. A. Probyn1,*, M. Pretorius2, K. Seanego1, A. Bernatzeder2 1Aquaculture Research and 2Sustainable Aquaculture Management, Department of Agriculture, Forestry and Fisheries, Private Bag X2, Vlaeberg 8018, Cape Town, South Africa *Corresponding author: trevorp@daff.gov.za ABSTRACT: Effluent water quality was measured at 9 abalone (Haliotis midae) farms in 2 regional nodes (west and south) along the South African coastline. For most farms, effluent total suspended solids (TSS) exceeded the background reference level (80th percentile), and 3 did not comply with the 5 mg l-1 standard. Total ammonia nitrogen (NH4+) concentrations were mostly greater than reference levels but well below the 43 µmol N l-1 standard. Inflow-corrected concentrations of nitrate, nitrite and phosphate were low compared to NH4+ and would not pose a significant eutrophication risk. Similarly, the biochemical oxygen demand measured at 3 of the farms was low (median 1.31 mg l-1). Abalone production-specific annual loads of TSS (334 kg per metric tonne [mt]), total N (20.3-38.1 kg N mt-1) and total P (3.2-7.5 kg P mt-1) agree with what has been found for different land-based aquaculture operations. These figures translate to N-based human population equivalents of 5.4-10.6 persons mt-1 for both regions. At the broader ecosystem level, the annual TSS loads calculated from 2013 production data of 43 mt yr-1 (west) and 369 mt yr-1 (south) are, respectively, 0.35 and 2.8% of that estimated for kelp erosion. Similarly, the dissolved inorganic N loads of 1.9 mt N yr-1 (west) and 9.4 mt yr-1 (south) are trivial by comparison with nitrate advected during upwelling. Local abalone farms have a relatively high specific C footprint—conservatively ~44 kg CO2 kg-1 production. Our findings support a relatively low potential impact of farm effluents in this coastal upwelling environment. KEY WORDS: Abalone farm · Effluents · Suspended solids · Nutrients · Haliotis Full text in pdf format PreviousNextCite this article as: Probyn TA, Pretorius M, Seanego K, Bernatzeder A (2017) Characterisation of water quality in effluents of land-based abalone farms in the Western Cape, South Africa. Aquacult Environ Interact 9:87-102. https://doi.org/10.3354/aei00217 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in AEI Vol. 9. Online publication date: February 21, 2017 Print ISSN: 1869-215X; Online ISSN: 1869-7534 Copyright © 2017 Inter-Research.

Efficient Utilization of Waste Carbon Source for Advanced Nitrogen Removal of Landfill Leachate

A modified single sequencing batch reactor (SBR) was developed to remove the nitrogen of the real landfill leachate in this study. To take the full advantage of the SBR, stir phase was added before and after aeration, respectively. The new mechanism in this experiment could improve the removal of nitrogen efficiently by the utilization of carbon source in the raw leachate. This experiment adopts the SBR process to dispose of the real leachate, in which the COD and ammonia nitrogen concentrations were about 3800 mg/L and 1000 mg/L, respectively. Results showed that the removal rates of COD and total nitrogen were above 85% and 95%, respectively, and the effluent COD and total nitrogen were less than 500 mg/L and 40 mg/L under the condition of not adding any carbon source. Also, the specific nitrogen removal rate was 1.48 mgN/(h·gvss). In this process, polyhydroxyalkanoate (PHA) as a critical factor for the highly efficient nitrogen removal (>95%) was approved to be the primary carbon source in the sludge. Because most of the organic matter in raw water was used for denitrification, in the duration of this 160-day experiment, zero discharge of sludge was realized when the effluent suspended solids were 30–50 mg/L.

Dynamic modelling of solids in a full-scale activated sludge plant preceded by CEPT as a preliminary step for micropollutant removal modelling.

The presence of micropollutants in the environment has triggered research on quantifying and predicting their fate in wastewater treatment plants (WWTPs). Since the removal of micropollutants is highly related to conventional pollutant removal and affected by hydraulics, aeration, biomass composition and solids concentration, the fate of these conventional pollutants and characteristics must be well predicted before tackling models to predict the fate of micropollutants. In light of this, the current paper presents the dynamic modelling of conventional pollutants undergoing activated sludge treatment using a limited set of additional daily composite data besides the routine data collected at a WWTP over oneyear. Results showed that as a basis for modelling, the removal of micropollutants, the Bürger-Diehl settler model was found to capture the actual effluent total suspended solids (TSS) concentrations more efficiently than the Takács model by explicitly modelling the overflow boundary. Results also demonstrated that particular attention must be given to characterizing incoming TSS to obtain a representative solids balance in the presence of a chemically enhanced primary treatment, which is key to predict the fate of micropollutants.

Pretreatment of Petrochemical Secondary Effluent by Micro-flocculation and Dynasand Filtration: Performance and DOM Removal Characteristics

A pilot scale micro-flocculation and dynasand filtration process was used to pretreat the petrochemical secondary effluent. The suspended solids (SS) and the dissolved organic matter (DOM) removal characteristics were investigated. The results showed that the optimized poly aluminum ferric chloride (PFAC) dosage was 10 mg/L during the experiment. In this dosage period, the SS removal rate was as high as 50.58 % with the effluent SS of 15.38 mg/L when the influent SS was 33.53 mg/L. The COD removal rate was 10.42 %. The DOM fraction with large apparent molecular weight (MW) higher than 3 k was removed more significantly than that of small molecular DOM. Resin fractionation showed that the micro-flocculation and dynasand filtration process could preferentially remove the hydrophobic neutrals (HON) and hydrophobic acids (HOA) of DOM, so it could be suitable as the pretreatment unit. When oxidized by catalytic ozonation, the ozone consumption of COD removal for filtrated effluent was 1.2 g-O3/g-COD while it was 1.6 g-O3/g-COD for untreated petrochemical secondary effluent, saving 25 % of ozone consumption. The micro-flocculation and dynasand filtration is a suitable pretreatment process for petrochemical secondary effluent, especially when the subsequent unit is the catalytic ozonation process.

Microalgae recycling improves biomass recovery from wastewater treatment high rate algal ponds

Microalgal biomass harvesting by inducing spontaneous flocculation (bioflocculation) sets an attractive approach, since neither chemicals nor energy are needed. Indeed, bioflocculation may be promoted by recycling part of the harvested microalgal biomass to the photobioreactor in order to increase the predominance of rapidly settling microalgae species. The aim of the present study was to improve the recovery of microalgal biomass produced in wastewater treatment high rate algal ponds (HRAPs) by recycling part of the harvested microalgal biomass. The recirculation of 2% and 10% (dry weight) of the HRAPs microalgal biomass was tested over one year in an experimental HRAP treating real urban wastewater. Results indicated that biomass recycling had a positive effect on the harvesting efficiency, obtaining higher biomass recovery in the HRAP with recycling (R-HRAP) (92–94%) than in the control HRAP without recycling (C-HRAP) (75–89%). Microalgal biomass production was similar in both systems, ranging between 3.3 and 25.8 g TSS/m2d, depending on the weather conditions. Concerning the microalgae species, Chlorella sp. was dominant overall the experimental period in both HRAPs (abundance >60%). However, when the recycling rate was increased to 10%, Chlorella sp. dominance decreased from 97.6 to 88.1%; while increasing the abundance of rapidly settling species such as Stigeoclonium sp. (16.8%, only present in the HRAP with biomass recycling) and diatoms (from 0.7 to 7.3%). Concerning the secondary treatment of the HRAPs, high removals of COD (80%) and N-NH4+ (97%) were found in both HRAPs. Moreover, by increasing the biomass recovery in the R-HRAP the effluent total suspended solids (TSS) concentration was decreased to less than 35 mg/L, meeting effluent quality requirements for discharge. This study shows that microalgal biomass recycling (10% dry weight) increases biomass recovery up to 94% by selecting the most rapidly settling microalgae species without compromising the biomass production and improving the wastewater treatment in terms of TSS removal.

Large scale tertiary filtration – results and experiences from the discfilter plant at the Rya WWTP in Sweden

This paper summarizes the results and experiences from the full-scale discfilter plant at the Rya WWTP. In 2010 the WWTP was extended with post-denitrification and a discfilter plant for tertiary filtration of the effluent in order to meet the new discharge limits of 10 mg total nitrogen and 0.3 mg/l of total phosphorus. The disc filters receive effluent from both the moving bed biofilm reactor (MBBR) and the secondary settlers. The disc filters are equipped with filter cloths with 15 µm pore openings. The concentration of suspended solids was generally kept below 5 mg/l and total phosphorus was <0.2 mg/l for approximately 60% of the days during the experimental period, with generally lower concentration of particles in the effluent from the disc filters during the summer. The mass load of suspended solids from the MBBR was higher compared to the load from the secondary settlers but this did not influence the concentration of suspended solids in the effluent from the disc filters. The particles in the MBBR effluent are larger and easier to filter compared to the secondary settler effluent which contain a larger number of small particles. During passage through the disc filters, some particles break-up leaving a larger number of particles (1–5 µm) in the effluent. Due to their small mass, this does not affect the effluent suspended solids concentration significantly. The removal of indicator and pathogenic microorganisms was only marginal. Since the discfilter plant has been placed in operation, the operational strategies have improved (e.g. more frequent cleaning of the filter cloths) which has increased the treatment capacity. The study demonstrates successful operation of a large discfilter plant with large variation in flow and particle loading.

Improvement and prediction of OSA system performance in sludge reduction through integration with thermal and mechanical treatment

The oxic-settling-anoxic (OSA) process is one of the sludge production reduction methods in the activated sludge process. In this method, sludge is stored in an anaerobic tank within the sludge return line before entrance into an aeration tank. Due to this method's flexibility in application to operating treatment plants and not being energy-consuming, its application is developing. In this research, the improvement of the OSA process is investigated via thermal and mechanical treatment in a sequencing batch reactor (SBR). A pilot-scale reactor and domestic wastewater are used. Sludge was subjected to high temperature in an anaerobic tank using a heat transformer and it was subjected to mechanical shear through mechanical mixing in the anaerobic tank. Different temperatures and voltages were tested. The OSA process reduced sludge production by 24% while the chemical oxygen demand (COD) removal rate decreased from 90% to 86%. Thermal treatment combined with the OSA process caused a maximum of 46% sludge production reduction. However temperatures above 90 °C are not recommended due to a high level of decrease in COD removal. Mechanical mixing in combination with the OSA process led to 34% sludge production reduction. The effluent quality is not affected by the OSA process itself but is slightly reduced by thermal treatment and mechanical mixing. Therefore, for reaching the maximum sludge reduction in OSA plus thermal and mechanical treatment it would be necessary to evaluate the effect of different sets of parameters on effluent quality beside the sludge reduction. For this purpose multi-layer perceptron artificial neural network models are developed to predict the effluent total suspended solids and COD removal efficiency as well as sludge production rate. The models perform well and would be useful tools in determining the optimal set of system operation parameters.

Submerged bed versus unsaturated flow reactor: A pressurized hydrogenotrophic denitrification reactor as a case study

The paper compares the main features of a submerged bed reactor (SuBR) with bubbling and recirculation of gas to those of an unsaturated flow reactor (uSFR) with liquid recirculation. A novel pressurized closed-headspace hydrogenotrophic denitrification system characterized by safe and economic utilization of H2 gas was used for the comparison.Under similar conditions, denitrification rates were lower in the SuBR as a result of a lower effective biofilm surface area and overall gas-liquid mass transfer coefficient kLa. Similar values of effluent DOC were achieved for both reactors, although effluent suspended solids concentration of the SuBR were substantially higher. On the other hand, the required cleaning frequency in the SuBR was 2.5 times lower. Moreover, the SuBR is expected to reduce the recirculation energy consumption by 0.35 kWh/m3 treated.

Performance of constructed wetland applied for domestic wastewater treatment: Case study at Boimorto (Galicia, Spain)

The study aims at evaluating the performance of a horizontal subsurface flow constructed wetland used for secondary treatment of domestic wastewater since May 2011 at Galicia (Spain). A septic tank was used as primary treatment. The wetland consists of two cells in parallel: cell-A with 350m2 and cell-B with 280m2, constructed with a depth of 0.6m, filled with gravel of 30mm of average size and planted with common reeds. The performance of wastewater treatment was controlled from June 2011 to September 2015. The rural agglomeration is served by a gravity sewer system with high rates of infiltration/inflow during wet weather. Thus, concentration and flow rate of wastewater have high seasonal variability. Average primary effluent BOD5, COD, suspended solids (TSS), total nitrogen (TN) and total phosphorous (TP) concentrations (in mg/L) were: 105, 197, 43, 29 and 3.4, respectively. Meanwhile, average secondary effluent BOD5, COD, SS, TN and TP values (in mg/L) were: 19, 44, 12, 14.3 and 1.9, respectively. A 2.2 log unit reduction for faecal coliforms was observed in the global system. The wetland required to be harvested at the end of each October. The sludge produced by the septic tank has not yet required to be removed. The wetland system presented no problems for vectors or nuisance odours.

Continuous electrocoagulation process for the post-treatment of anaerobically treated municipal wastewater

The potential of continuous electrocoagulation (EC) process with aluminium electrodes for the post-treatment of upflow anaerobic sludge blanket (UASB) reactor-treated municipal wastewater was investigated. In order to optimise the performance, influence of three parameters affecting EC, namely, chemical oxygen demand (COD), current density (CD) and residence time in the reactor was studied using response surface methodology (RSM) with Box–Behnken design (BBD) employing real UASB reactor effluent. The results of the modelling study gave the following optimum conditions: influent COD concentration 274mg/L, CD 2mA/cm2 and residence time 5min; and predicted effluent COD, phosphate and turbidity values of 87mg/L, 0.59mg/L, and 12.6NTU, respectively. Confirmatory tests at these optimum conditions gave 90mg/L effluent COD, 0.57mg/L effluent phosphate and 15.2NTU effluent turbidity, which were in close agreement with the predicted results. At optimum conditions, high removals of BOD and suspended solids were also observed, with effluent BOD and suspended solids concentration of 34mg/L and 29mg/L, respectively. High total coliform and faecal coliform removals of 99.81% and 99.86%, respectively, were also obtained at these conditions. The study thus suggests EC as an attractive post-treatment option for UASB reactor-treated municipal wastewater.

Evaluation of a Point-of-Use Electrocoagulation System for Arsenic Removal

A point-of-use prototype electrocoagulation treatment system was designed and evaluated for its ability to remove arsenic from a synthetic groundwater. The system was comprised of an electrocoagulation reactor providing batch treatment, a rechargeable battery power source, an electrical monitoring and control module, and a granular media filter. The control module and the filter underdrain system were designed to improve user convenience. The system was able to consistently reduce arsenic concentrations to below 20 µg/L. Effluent soluble arsenic concentrations under 10 µg/L were deemed possible with enhanced effluent suspended solids removal techniques. Arsenic removal was found to be a function of the initial arsenic concentration and the cumulative charge dosage as measured in coulombs per liter of water treated. The steel plate size used in the electrocoagulation module influenced the current draw and the overall electrical efficiency of the system. The monitoring and control module allowed the system to produce up to 100 liters of treated water daily on a single battery charge and would automatically control charge and iron dosage. The point-of-use system was capable of meeting household potable demands for water where other treatment options are limited.