Final Effluent Concentrations Research Articles

Treatment of effluents from Food Services Establishment (FSEs) by physico-chemical processes: a case study for Trinidad & Tobago

BackgroundEffluents from Food Services Establishments (FSEs) contain primarily Fats, Oil and Grease (FOG) which severely impact on sewers and the environment when released in high concentrations. In Trinidad & Tobago, it is estimated that approximately 231,304 kg/day of unaccounted for FOG bearing wastewaters from FSEs, are released into the environment with no viable treatment in the country. This research explored the optimization of physico-chemical processes for the treatment of FOGs for subsequent release into sewers.ResultsBench-scale studies analysed the characteristics of FSE’s effluents from three popular sources, conducted the treatment of these effluents using Jar Tests, and subsequently confirm results via a pilot plant study. Characterization showed the mean concentration of the parameters examined to be; FOG (511 mg/l ± 116 mg/l), Suspended Solids (446 mg/l ± 146 mg/l), Chemical Oxygen Demand (2229 mg/l ± 963 mg/l) and pH (6 ± 0.3). Jar Tests were conducted using Poly-aluminium Chloride (PACl) as coagulant, anionic and cationic polyelectrolytes as flocculant aids with suitable pH adjustments of samples to determine the isoelectric point for the coagulant. Effluent results showed FOG removal levels of 99.9% and final effluent concentration of 0.17 mg/l. This was attained using PACl concentration of 250 mg/l, a 0.1% low cationic polyelectrolyte (CP 1154) at 4 mg/l with the pH of sample adjusted to 8. The pilot plant achieved a 97.4% removal of FOG (residual of 16.8 mg/l) using the same coagulant dosing, and pH value, but increasing the strength of the flocculant aid to 0.1% medium cationic (CP1156) at 5 mg/l.ConclusionExperimentation showed high concentrations of emulsified FOG can be efficiently removed to levels below the permissible requirements (20 mg/l) for entry into sewer systems in Trinidad and Tobago using coagulation, flocculation and sedimentation techniques. Pilot scale study also revealed that a higher strength and/or dose of the cationic polyelectrolyte and increased times in primary and final tanks were required to attain the desired results as in the bench level study, where equipment limitations in the flocculation tank were faced. This is in alignment with theory where factors critical for agglomeration is equipment type and density charge. It is, concluded that the optimum combination of chemicals and the respective dosages attained at the bench level study should prove effective should the right equipment be made available.

Study of Ammonia-Nitrogen and Phosphorus in Parit Rasipan Canal During the Wet Season

The Parit Rasipan Canal's deteriorating water quality and eutrophication are both blamed on ammonia-nitrogen and phosphorus. In order to conserve freshwater resources, it is crucial to understand the relationship between land use and water quality. It is also crucial to evaluate how land use affects the pollutants load. In this study, eutrophication along the Parit Rasipan drainage system will be identified, water quality will be investigated in terms of phosphorus and ammonia nitrogen concentration and classified according to land use type during the wet season, and ammonia-nitrogen and phosphorus concentrations will be compared with Normalized Difference Vegetation Index (NDVI) using unmanned aerial vehicles (UAV). At a specific location along the Parit Rasipan drainage system, samples were taken. The USEPA PhosVer 3 (Method 8190) and Nessler's Method (Method 8038) were used, respectively, to measure phosphorus and ammonia nitrogen. Ammonia nitrogen and phosphorus final effluent concentrations ranged from 3.21 mg/L to 5.96 mg/L and 0.36 mg/L to 1.55 mg/L, respectively. The residential area's water, on the other hand, had significant concentrations of ammonia, nitrogen, and phosphorus, which contributed to eutrophication in the wake of industrial, agricultural, and farming activities.

Performance of olive mill wastewater treatment using hybrid system combining sand filtration and vertical flow constructed wetlands

Olive mill wastewater (OMWW) is a main source of noxious and recalcitrant organic pollutants of significant concern in environmental engineering. For this purpose, the current study assessed the performance of system combining sand filtration and vertical flow constructed wetlands (VF-CWs) in reducing the organic load of OMWW. Sand filter system wed in this study is composed of 6 plastic columns of 0.50 m in diameter and 120 L of capacity. The irrigation of sand filter columns was assured by 50 % diluted OMWW at flow rate of 5 L/day. VF-CWs system consists of a 1 m3 tank filled with soil and gravel in the bottom and planted of Typha latifolia, Phragmites australis and Arundo donax aquatic plants. The irrigation of VF-CWs system was assured with treated OMWW with a flow rate of 20 L twice in the week. Obtained results showed that sand filtration achieved a high removal rate of 76.42, 75.12, 79.7 and 78.10 %, respectively, for total suspended solid (TSS), dissolved COD (chemical oxygen demand), total COD and phenolic compounds. The usage of the combination of sand filter and VF-CWS improved significantly the elimination efficiency of total COD up to 91.44 %, dissolved COD up to 77.09 % and phenolic compounds up to 79.47 %, but it did not report any performance in the removal of TSS. Despite the high performance of hybrid system (sand filter+VF-CWs) in reducing the organic pollution, final effluent concentrations remained below the permitted limits for discharge into a municipal sewer system.

Removal of organic matter and nutrients from hospital wastewater by electro bioreactor coupled with tubesettler

Wastewater consisting of different pharmaceuticals and drug residues is quite challenging to treat and dispose of. This situation poses a significant impact on the health aspect of humans and other biotic organisms in the environment. The main concern of hospital wastewater (HWW) is the resistivity towards treatment using the different conventional methods. For the treatment of HWW, this study was performed using an electro bioreactor using hospital wastewater. The electro reduction overcomes the effect of toxic elements in hospital wastewater, and biodegradation removes organic matter and nutrients from wastewater. This study investigated electro bioreactor performance for treating hospital wastewater connected with tubesettler. The parameters of chemical oxygen demand, nitrate, and phosphate concentration were analyzed to evaluate an influent and effluent from electro bioreactor and tubesettler. Also, Kinetic modelling for chemical oxygen demand, nitrate, and phosphate removal was done. The chemical oxygen demand was reduced by 76% in electro bioreactor, and 31% in tubesettler, 84%. The nitrate and phosphate were reduced within permissible discharge limits with a final effluent concentration of 1.4 mg L−1 and 3 mg L−1. Further studies are required to assess the impact of pharmaceutical compounds in hospital wastewater on the system's performance.

Removal of cyanide from alumina smelter wastewater using precipitation and filtration technique

Aluminum is a metal that is used in many products because of its good conducting properties. However, in the production process, aluminum is not obtained easily but through a long process. In aluminum smelting process, wastewater that is produced indicates the existence of pollutants as determined by several indicators of water pollution, one of which is cyanide that will threaten human and environmental health if not treated properly. This study was conducted to determine the optimal dose of ferrous sulfate to remove cyanide, the precipitation and filtration process efficiency in reducing cyanide, and its effect on pH of wastewater. Data were collected from an aluminum smelting company, and experiments were conducted in the laboratory. Based on results, ferrous sulfate dose of 93 mg/l is the most optimal dose in removing cyanide with an efficiency of 58.74±0.51%, while filtration process provides an efficiency of 81.65±0.42%. Precipitation with ferrous sulfate makes pH value of wastewater decrease, but filtration process increases the value again. Throughout the whole process, cyanide can be reduced by a combination of precipitation and filtration process with the efficiency of 92.43±0.26% and an average final effluent concentration of 0.78 mg/L from an initial concentration of 10.3 mg/L.

Investigating the chromium status, heavy metal contamination, and ecological risk assessment via tannery waste disposal in sub-Saharan Africa (Kenya and South Africa).

To mitigate the negative environmental and public health concerns associated with increased industrial discharges amid the rapid industrial growth, sub-Saharan African countries have instituted several environmental regulations and policies. However, a paradox of good environmental policies but inadequate enforcement exists in most of these countries, with information on the pollution level unknown due to poor monitoring resources. In this study, potentially toxic heavy metal contamination and physicochemical characteristics in effluents and dumpsite soils of two tanneries in Kenya (DB) and South Africa (BO) were evaluated during the dry and rainy season of 2018. Pollution levels and ecological risk in the dumpsite soils were assessed by adopting geoaccumulation index (Igeo), contamination factor (CF), pollution load index (PLI), and ecological risk index (PRI). The results showed that the mean final effluent concentration fortotal dissolved solids (TDS), chemical oxygen demand (COD), and Cr, Cu, Fe, Ni, Zn, and Cd for BO (2127, 890, 1.82, 1.38, 1.96, 0.60, 1.21, and 1.16, respectively) and DB tanneries (8157, 1369, 7.90, 0.69, 1.05, 0.60, 1.72 mg/L, respectively) were above the limits of emission guidelines. The mean Cr and Cr(VI) concentrations in tannery dumpsite soils (204.9 ± 29.1 and 0.31 ± 0.01 and 943 ± 29.8 and 0.4 ± 0.07 mg/kg for BO and DB, respectively) and Fe (2498 ± 62 mg/kg in DB) exceeded acceptable thresholds of the World Health Organization (WHO), Food and Agriculture Organization (FAO), and local background levels. A positive strong correlation was observed between Cr and organic matter, OM (r > 0.7, p < 0.001), electrical conductivity, EC (r=0.99, p < 0.05), and As (r = 0.62; p < 0.05), suggesting a common anthropogenic point source. The mean PLI values of 5.3 and 1.6 for DB and BO dumpsites indicated significant pollution of the soils with heavy metals, specifically Cr (Igeo = 18 and 2.4 for DB and BO, respectively). Similarly, PRI values of 174.8 and 57.4 indicated a moderate and low potential ecological risk for DB and BO tannery dumpsite, respectively, with several plants sampled within the two sites exhibiting elevated levels of Cr contamination. In summary, these results provide scientific insights on the need for both improved effluent management and treatment technologies of tannery wastes, coupled with the strengthening of continuous monitoring and enforcement for compliance of industrial discharges in sub-Saharan countries.

Novel Treatment of Sugar Mill Wastewater in a Coupled System of Aged Refuse Filled Bioreactors (ARFB): Full-Scale

Sugar is the most important food supplement of our daily diet. During the production, sugar mills use a large volume of water and produce a significant amount of wastewater polluted with high organic compounds. Therefore, it is necessary to treat the wastewater before their disposal. For this reason, this article presents the results obtained from the monitoring of a coupled system of aged refuse filled bioreactors (ARFB) in full scale to treat wastewater from a sugar mill. The coupled system consists of two bioreactors (a primary one -ARFB1- and a rectification one -ARFB2-) arranged in a series with identical geometries. The ARFB1-ARFB2 system was evaluated in two stages. The first stage (maintenance period) for 28 weeks, and second stage (Zafra season) for 29 weeks. The system was fed with sugar mill wastewater (SMW) with a chemical oxygen demand (COD) of 2787 ± 1552 mg/L and 2601 ± 722 mg/L, respectively. As results, we observed a rapid stabilization of the system over 2 months. In addition, we found the ARFB1-ARFB2 system achieved an average COD removal of 94.9%, with a final effluent (E2) concentration below the maximum permissible limits of Mexican and international regulations for all analyzed parameters. Finally, the results of this study show that the ARFB1-ARFB2 full-scale novel technology is an efficient process for removal of the main contaminants that affect the wastewater from the sugar mills.

Removal of persistent organic contaminants from wastewater using a hybrid electrochemical-granular activated carbon (GAC) system

A three-dimensional (3D) electrochemical flow-through reactor equipped with GAC packed bed, polarized by the electric field, was evaluated for the removal of persistent organic contaminants from real sewage effluent. The performance of the reactor was investigated for 27 consecutive runs at two anodic current densities, i.e., low current density (LCD) of 15 A m−2, and high current density (HCD) of 100 A m−2. In the HCD experiments, the adsorption ability of saturated GAC was increased, mainly due to the increase in the mesoporosity of GAC. A synergy between electrosorption/adsorption on GAC and electrooxidation was observed in terms of the removal of all target pollutants. DEET presented the highest synergy, ranging from 40% to 57%, followed by iopromide (22–46%), carbamazepine (15–34%) and diatrizoate (4–30%). The addition of GAC decreased the concentrations of toxic chlorate and perchlorate by 2-fold and 10-fold, respectively, due to their electrosorption on GAC. Also, 3D electrochemical system yielded lower concentrations of adsorbable organic iodide (AOI) and adsorbable organic chlorine (AOCl). Thus, addition of low amounts of GAC in electrochemical systems may be a low-cost and simple way of minimizing the formation and final effluent concentrations of toxic halogenated byproducts.

Decentralized grey and black water reuse by combining a vertical flow constructed wetland and membrane based potable water system: Full scale demonstration

Safe drinking water is not accessible in many rural and peri-urban areas. Decentralized wastewater treatment can be a sensible solution for communities of any size and/or demographic having a very small water cycle and could be used as a solution to provide potable water at more remote locations. In view of demonstrating decentralized production of potable water, a hybrid system combining a vertical flow constructed wetland (VFCW) and a membrane filtration system was designed and operated at a restaurant. The VFCW with an area of 60 m2 was constructed and operated for six months at a hydraulic loading rate of 0.05 to 0.08 m3. m−2.d-1 and achieved a removal of 84%, 97%, 92%, 42% and 24% for chemical oxygen demand (COD), biological oxygen demand (BOD), total suspended solids (TSS), total nitrogen (TN) and total phosphorus (TP) respectively, corresponding to mass loading rates of 9.6 gCOD. m−2.d−1, 7.9 gBOD. m−2.d−1, 4.7 gTSS. m−2.d−1, 1.5 gTN. m−2.d−1. Final (average) effluent concentrations were 7 mg.L−1, 1.6 mg.L−1, 4.7 mg.L−1, 1.5 mg N.L−1 and 1.5 mg P.L−1 for respectively COD, BOD5, TSS, TN and TP. The VFCW effluent was further treated using a combination of activated carbon, ultrafiltration, reverse osmosis and mixed bed ion exchange, remineralization as well as ultraviolet disinfection to produce potable water. This potable water met the legislative criteria and was used in the restaurant for drinking and cleaning purposes. As such, a sustainable decentralized potable water system with direct black water reuse was demonstrated at full-scale.

Construction of Mass Balances of Cocaine in Batch Studies for the Sewage Treatment Works

The desired approach at safeguarding the environment both in control and effective monitoring of chemical discharges is the use of mass balances to account for inflow/outflow of pollutants. Whereas the previous studies were based on several assumptions, the batch studies enabled the construction of mass balances for the Sewage Treatment Work (STWs) using the removal rate data. This study, for the first time measures the rates of removal of cocaine in an STW, and the calculated mass balances were obtained from the removal rate data that were generated. The result of cocaine initial influent of 50 mg L-1 after after 2 hour hydraulic retention times (HRT) produced the final effluents of 110 mg L-1. Projected influent concentrations of cocaine (14, 471 ng L-1) were derived from back-calculation from final effluent concentrations. A useful tool that accounts for the mass-flow of trace drugs in the aquatic environment with minimal errors often due to sampling logistics and desludging process has been provided in this model of mass balance calculations in STWs. &#x0D; Keywords: removal rate, effluent, influent, mass balance, sewage treatment work, cocaine

Assessment of brewery wastewater treatment by an attached growth bioreactor

Abstract Craft beer is a rapidly growing market globally, placing an increased burden on wastewater treatment plants. To avoid discharge fees, new technology is required to make the on-site treatment of brewery wastewater affordable. This study assessed the application of a novel attached growth bioreactor (AGBR) to treat brewery wastewater to a discharge target (1,500 mg sCOD/L). Specifically, the impacts of the single-pass residence time (HRTsingle-pass), organic loading and media height were investigated. A HRTsingle-pass of 67 min demonstrated the shortest required time to meet the discharge target and the lowest final effluent concentration after 120 hr treatment time. Long HRTsingle-pass demonstrated slower biomass development, while smaller HRTsingle-pass caused an earlier rise in dissolved oxygen (DO) which hindered organic removal by heterotrophic bacteria. The sCOD removal rate increased with loading rates, however plateaued at 65 g sCOD/m2/day for loading rates above 300 g sCOD/m2/day. The media became flooded with biomass for feed strengths above 6.0 g sCOD/L. Greater media height provided additional surface area for biomass development, but marginally decreased the sCOD removal rate (g/m2/day) due to an earlier introduction of DO. Power consumption and footprint considerations found the greater media height to be the preferred choice for breweries.

Performance analysis and life cycle greenhouse gas emission assessment of an integrated gravitational-flow wastewater treatment system for rural areas

Due to the lack of appropriate wastewater treatment facility in rural areas, the discharging of wastewater without sufficient treatment results in many environmental issues and negative impact on the local economy. In this study, a novel integrated gravitational-flow wastewater treatment system (IGWTS) for treating domestic wastewater in rural areas was developed and evaluated. As the core module of IGWTS, the multi-soil-layering (MSL) system showed good performances for removing organic matters and nutrients in lab-scale experiments. Aeration was found to be the dominant positive factor for contaminant removal in factorial analysis, while bottom submersion had the most negative effect. Based on the critical operational factors obtained from lab-scale tests, the full-scale IGWTS consisting of multifunctional anaerobic tank (MFAT), MSL, and subsurface flow constructed wetland (SFCW) was designed, constructed, and operated successfully in the field application. The final effluent concentrations of COD, BOD5, TP, NH3-N, and TN reached 22.0, 8.0, 0.3, 4.0, and 11.0mg/L, with removal rates of 92, 93, 92, 86, and 76%, respectively. The feasibility of IGWTS was also quantitatively evaluated from the perspectives of resource consumption, economic costs, water environment impact, and life cycle greenhouse gas (GHG) emissions. IGWTS has been proved to be a sound approach to mitigate GHG emissions compared with centralized wastewater treatment plant. It can also be featured as an eco-friendly technology to improve rural water environment, and an economic scenario with low construction and operation costs. Graphical abstract.

Anaerobic and aerobic sewage treatment plants in Northern India: Two years intensive evaluation and perspectives

Abstract The present study investigates the long term treatment performance of seven different sewage treatment plants located in different cities of north India for over a period of two years; two treatment technologies based on intensive aerobic processes — sequencing batch reactor (SBR) and moving bed bio-film reactor (MBBR) and; three combination of Up-flow Anaerobic Sludge Bed (UASB) reactor followed by aerobic processes — Polishing Ponds (PP), Aeration + PP and Down-flow Hanging Sponge (DHS). Effluent quality was not in accordance to the surface water disposal standards, Ministry of Environment, Forest and Climate Change Govt. of India, for UASB followed by PP and by Aeration +PP. However, a high effluent quality was observed in UASB followed by DHS; SBR and MBBR systems. In the last cases, NH4-N and PO4-P removal was higher than 85 and 60%, respectively; with a final effluent concentration of 20 mg BOD5/L, 50 mg COD/L, 20 mg TSS/L, 10 mg NH4-N/L and 5 mg PO4-P/L. Although strictly intensive aerobic systems showed a better performance, UASB followed by simple aerobic systems, such as the DHS process is a promising technology, especially in India to reach required BOD level for water reuse at low costs.

Whether glycine betaine improves the thermotolerance of mesophilic anammox consortia

ABSTRACT While the application of mesophilic anammox process is currently the state of the art, the feasibility of a thermophilic anammox bioprocess is still unclear. In this study, we investigate whether glycine betaine (GB) addition can enhance the thermotolerance of mesophilic anammox biomass in the upflow anaerobic sludge blanket (UASB) reactors fed with synthetic wastewater at a nitrogen loading of approximately 4 kg N m–3 d−1. The results showed that during a long-term operation at 45°C with GB (0, 0.1, 1, 2 mM) addition, anammox performance became worse with the final effluent concentrations of NO2 –N of 145 ± 11.6 mg L−1 and nitrogen removal efficiency decreased from 92.3–6.9%. Specific anammox activity decreased from 392.1 ± 12.1–6.0 ± 0.8 mg N g−1 VSS d−1, which were not significantly higher than those in the control reactor. The content of heme c showed a stronger downward trend in T1 (with GB addition) than in the control reactor T0. The qPCR results showed that the relative abundance of Candidatus Kuenenia decreased in both the experimental (from 53.5–28.8%) and control reactors (from 54.1–35.1%). Overall, continuous addition of exogenous GB did not improve the thermotolerance of mesophilic anammox consortia at 45°C.

A hybrid constructed wetland for organic-material and nutrient removal from sewage: Process performance and multi-kinetic models

A pilot-scale hybrid constructed wetland with vertical flow and horizontal flow in series was constructed and used to investigate organic material and nutrient removal rate constants for wastewater treatment and establish a practical predictive model for use. For this purpose, the performance of multiple parameters was statistically evaluated during the process and predictive models were suggested. The measurement of the kinetic rate constant was based on the use of the first-order derivation and Monod kinetic derivation (Monod) paired with a plug flow reactor (PFR) and a continuously stirred tank reactor (CSTR). Both the Lindeman, Merenda, and Gold (LMG) analysis and Bayesian model averaging (BMA) method were employed for identifying the relative importance of variables and their optimal multiple regression (MR). The results showed that the first-order–PFR (M2) model did not fit the data (P > 0.05, and R2 < 0.5), whereas the first-order–CSTR (M1) model for the chemical oxygen demand (CODCr) and Monod–CSTR (M3) model for the CODCr and ammonium nitrogen (NH4−N) showed a high correlation with the experimental data (R2 > 0.5). The pollutant removal rates in the case of M1 were 0.19 m/d (CODCr) and those for M3 were 25.2 g/m2∙d for CODCr and 2.63 g/m2∙d for NH4-N. By applying a multi-variable linear regression method, the optimal empirical models were established for predicting the final effluent concentration of five days' biochemical oxygen demand (BOD5) and NH4-N. In general, the hydraulic loading rate was considered an important variable having a high value of relative importance, which appeared in all the optimal predictive models.

Microbial removal efficiency of a natural wastewater treatment system and the impact of its effluent on receiving waters

The discharge of untreated or partially treated wastewater into streams is a huge problem in developing countries in that it leads to severe environmental degradation, and, also, poses serious public health challenges to communities which live downstream. The study investigated the microbial removal efficiency of individual ponds of a waste stabilization pond system and the overall performance of the treatment systems in the removal of indicator bacteria and organic matter. The impact of the discharged effluent on the receiving waters was evaluated. The final effluent concentration of BOD and TSS were 1.7±1.2 and 10.1±4.3 mg/l, representing overall removal efficiencies of 98.7 and 98.6 percent, respectively. Overall log removal of faecal coliform (FC) and E. coli were 3.8, and 4.7 log units, representing a percentage removal of 98.4 and 99.8 percent, respectively. The mean diversity upstream was 0.11±0.09 while the downstream was 0.14±0.05, and this was not statistically different. The presence of macro-invertebrate families of Elmidae and Libellulidae downstream the point of discharge is an indication of good water quality

Hybrid natural systems for treatment of olive mill wastewater

AbstractBACKGROUNDThis study examines the efficiency of various natural systems in treating untreated OMW before it is discharged to the environment. The experimental set‐up consisted of two hybrid pilot‐scale natural systems. The first hybrid system (HS‐A) comprised two open tanks (OTs), one vertical flow (VF) constructed wetland (CW) and one free water surface flow (FWS) CW and the second one (HS‐B) comprised two OTs and one FWS CW.RESULTSRegarding the HS‐A system, TSS, COD, TKN and phenols (PHE) removals in the two OTs were 83.0%, 21.6%, 62.3% and 12.9%, and cumulative removals in the VF and FWS CW systems were 52.0%, 54.1%, 44.4% and 60.1%, respectively. Regarding the HS‐B system, TSS, COD, TKN and PHE mean removals in the two OTs were 80.7%, 32.2%, 64.1% and 24.7%, and in the FWS CW were 72.0%, 49.4%, 26.9% and 51.1%, respectively. The final pollutant effluent concentrations remained high for disposal in water bodies or reuse for irrigation; further reduction could be achieved by adding additional FWS CWs in series.CONCLUSIONHybrid natural systems can be used in efficiently and economically treating OMW. Such hybrid systems could be applied to small family‐owned olive oil producing enterprises to treat OMW economically. © 2017 Society of Chemical Industry

Upgrading and evaluation of a simple pond system for small communities with simple interventions to reduce land requirements and increase performance

The study covers different investigations related to the upgrading of a post-treatment system for the effluent from a upflow anaerobic sludge blanket reactor. The original post-treatment scheme comprised three ponds in series and a small coarse rock filter inserted in the last pond. Upgrading involved reducing the pond depths, applying baffles in the second pond and converting all of the third pond into a rock filter (three decreasing grain sizes). The system was conceived for 250 population equivalents, occupied an area of only 1.5 m2/inhabitant and aimed at very good removals of all major wastewater constituents. Overall final effluent concentrations for Biochemical Oxygen Demand (BOD), Chemical Oxygen Demand (COD) and Total Suspended Solids (TSS) were very good, and lower than those from the previous treatment line. Hydraulic flow patterns in both ponds showed daily thermal stratification and destratification periods. The conversion of the third pond into a rock filter increased the removal capacity of TSS (algae), but could potentially result in clogging, a phenomenon that was evaluated by a geophysical method called Georadar. The influence of accumulated sludge on treatment performance was tested before starting the operation of the upgraded system by operating the two ponds in parallel (one with sludge accumulated after 11 years of operation and the other without sludge). In this test, ammonia removal was virtually the same in both ponds.

Integrating pretreatment and denitrification in constructed wetland systems.

The aim of this work was to study the operational characteristics and the efficiency of a compact constructed wetland system for municipal wastewater treatment that integrates denitrification in the pre-treatment unit. The proposed system was simulated by two units in series with effluent recirculation, the first one being an anoxic digester, conceived as a hydrolytic up flow sludge bed for solids hydrolysis and denitrification, and the second one a sand column that simulated the operation of a vertical flow constructed wetland. The hybrid system consisted of two small columns of 4 and 10.2cm in diameter (anoxic digester and vertical flow unit, respectively). The unplanted system was operated successively with synthetic and real municipal wastewater over a period of 136days. Hydraulic loading rate ranged from 212 to 318mm/day and surface loading rate from 122 to 145g/m2·day of chemical oxygen demand and 10-15g/m2·day of total nitrogen for the overall system. The overall system reached removals of 91% to 99% for total suspended solids, chemical oxygen demand and biochemical oxygen demand whilst total nitrogen removal ranged from 43% to 61%. In addition to suspended solids removal (up to 78%), the anoxic digester provided high denitrification rates (3-12gN/m2·day) whilst the vertical flow unit provided high nitrification rates (8-15gN/m2·day). Organic matter was mainly removed in the anoxic digester (63-82% chemical oxygen demand) and used for denitrification. Final effluent concentration was lower for ammonia (7.4±2.4mgN/L on average) than for nitrate (19.8±4.4mgN/L), denitrification appearing as the limiting step in nitrogen removal in the system. CH4 or N2O emissions were not detected in any of the units of the system indicating very low greenhouse gas emissions.

Reuse of sewage treated effluent in agricultural practices: An alarming presence of Giardia spp. cysts

It was evaluated the removal efficiencies of Giardia spp. cysts and helminth eggs by a simplified system of wastewater treatment. The treated effluent was checked to be reused in agricultural practices. The system was composed by anaerobic filter and intermittent sand filter. Final effluent concentration was: COD of 52±24mgL−1, TSS of 17±20mgL−1 and low turbidity values (3±4 UT). The anaerobic filter could remove 99.7±28.7% of estimated cysts concentration in the raw sewage. The sand filter removed 38.0±31.6% of Giardia spp. cysts from the anaerobic effluent, inducing the total efficiency of the system to 99.8%. The system could also remove 100% of helminth eggs. However, we also identified 93±92 cysts L−1 in the final effluent. Thus, there is a necessity to further study these decentralized systems in order to prevent the spread of infectious parasites forms in agricultural practices.