Effluent Discharge Regulations Research Articles

Performance assessment of Mabula municipal wastewater plant: Zvishavane town, Zimbabwe

The characterisation and performance assessment of municipal wastewater treatment plants is very important as it provides information regarding the types of contaminants present in the water and their subsequent concentrations. It is also important in assessing gaps within the treatment process and is thus an essential step in needed when recalibrating and redesigning a plant to improve its efficiency. However, in Zimbabwe there is lack of comprehensive current data characterises effluent and influent from municipal wastewater treatment plants. The aim of the study was to assess the quality of wastewater from Mabula wastewater treatment plant, Zvishavane Zimbabwe, infer the performance of the plant and assess the implications of municipal effluent discharge on the water quality of Musavezi River. Composite water samples were collected over a 21-week sampling period from December 2022 to April 2023 from five sampling points, two from the treatment stages within the plant and three points along the course of the Musavezi River. Samples were taken to an independent laboratory and analysed for pH, Biological Oxygen Demand (BOD5), Chemical Oxygen Demand (COD), Total Suspended Solids (TSS), Total Nitrogen (TN), Total Phosphorous (TP) and Ammonium-Nitrate (NH3–N) in line with standards set by the American Public Health Association (APHA). Results from the study indicate that the plant receives and treats effluent that is of medium to high strength. Mean values of the effluent at discharge point indicated organic and nutrient concentrations that were higher than the Zimbabwe effluent discharge standards as prescribed by the Environmental Management Agency. Removal efficiencies for the plant varied from 83.01%, 83.02%, 88.26%, 36.21%, 67.43% and 51.6% for BOD5, COD, TSS, TN, TP, and NH3–N respectively. This indicates that the treatment plant is not performing very well with regards to nutrient removal. Effluent disposal was revealed to have implication on the water quality of the Musavezi River as indicated by water quality index (WQI). There is need to consistently monitor and regulate the performance of Mabula wastewater treatment plant so that it meets the national effluent discharge regulations.

Effluent Quality-Aware Event-Triggered Model Predictive Control for Wastewater Treatment Plants

Wastewater treatment plants (WWTPs) are large-scale and nonlinear processes with tightly integrated operating units. The application of online optimization-based control strategies, such as model predictive control (MPC), to WWTPs generally faces high computational complexity. This paper proposes an event-triggered approach to address this issue. The model predictive controller updates information and solves the optimization problem only when the corresponding triggered logic is satisfied. The triggered logic sets the maximum allowable deviation for the tracking variables. Moreover, to ensure system performance, the design of the event-triggered logic incorporates the effluent quality. By obtaining the optimal sequence for the effluent quality within the receding horizon of the MPC, the cumulative deviation between the predicted and desired effluent quality is analyzed to evaluate the performance within that horizon. Based on these two conditions, the need for adjusting control actions is determined. Even if the maximum allowable range for the tracking variables in the triggered logic design is set unreasonably, the consideration of effluent quality factors in the triggered conditions ensures good performance. Simulation results demonstrate an average reduction in computational effort of 25.49% under different weather conditions while simultaneously ensuring minimal impact on the effluent quality and total cost index and compliance with effluent discharge regulations. Furthermore, this method can be combined with other approaches to guarantee effluent quality while further reducing computation time and complexity.

A Review on Adsorption Process for the Treatment of Oily Wastewater

Oil-contaminated or oily wastewater (OW) is generated from various industrial and domestic premises. It consists of fats, oils, and greases and may contain petroleum fractions such as diesel oil, gasoline, and kerosene. It is regarded as one of the most hazardous wastewaters, causing serious environmental and health threats to ecosystems and human beings. The global increase in the discharge of OW coupled with stringent regulations for effluent discharge and incessant drive for the reuse of treated wastewater necessitate the need for the treatment of the OW. Conventional approaches employed in the past are inept for OW treatment due to low separation efficiency, high operational cost, creating secondary pollution, and long treatment hours. Comparatively, the adsorption process is considered a better alternative because of its simple design and can involve low investment in terms of both initial cost and land required. Thus, the adsorption process is widely applied as a promising alternative to existing treatment methods for OW. The adsorption process is an effective technique for OW treatment. Super adsorbents with ultrahigh adsorption capabilities are highly desired for efficient OW treatment in a new revolution of adsorption technology to meet present and future needs. This review provides insights into advanced and emerging state-of-the-art technologies of the adsorption process as a safe and efficient treatment of OW. Strength, weakness, opportunities and threats (SWOT) analysis was conducted to identify and analyze internal strengths and weaknesses and external opportunities and threats that shape the current and future operation of the adsorption process for the treatment of oily wastewater for developing strategic goals. Super adsorbents with ultrahigh adsorption capability such as P-GSC and P-PKS discussed are highly desired. The extraordinary properties of P-GSC and P-PKS can provide leap-forward opportunities to revolutionize traditional adsorption technology. However, scale-bridging and optimization study of these innovated super adsorbents is required for the real application. It shows a bright future of P-GSC and P-PKS towards OW treatment.

Characterization, Transformation, and Bioavailability of Dissolved Organic Nitrogen in Biofilters Treating Domestic Onsite Wastewater

This study investigated the transformation, bioavailability, and seasonal changes of dissolved organic nitrogen (DON) in nitrogen removing biofilters (NRBs) treating domestic onsite wastewater. The results demonstrated that NRBs were able to remove 92.6–94.3% DON from septic tank effluent with low effluent DON concentrations (0–5.8 mg N L–1), comparable to the levels detected in the tertiary municipal wastewater treatment plant. Both hydrophilic and hydrophobic DON were efficiently removed by the sand filters, while additional hydrophilic DON (0.8–1.8 mg N L–1) was produced in the lignocellulose/sand layer due to soluble microbial product formation. Seasonal change (i.e., temperature variation) did not impact the effluent DON composition or its removal efficiency by NRBs, while higher concentrations of hydrophilic DON (1.7–2.5 mg N L–1) were detected in the final effluent during the summer months (16.4–22.9 °C). DON in the NRB effluent had a higher potential to stimulate algal growth than other nitrogen forms (NH4+ and NOx–), confirmed by higher chlorophyll-a concentrations observed in the bioassay tests. The results suggest the DON levels in the final effluent of an onsite wastewater treatment system shall also be considered in onsite wastewater quality management and the effluent discharge regulations.

Simultaneous removal of single and mixed cationic/anionic dyes from aqueous solutions using flotation by colloidal gas aphrons

The treatment of dye-contaminated wastewater poses a challenge to industries due to stringent effluent discharge regulations. In this study, the removal of individual and mixed dyes from aqueous solutions using flotation by colloidal gas aphrons (CGAs) was investigated. The natural surfactant extracted from the leaves of the Ziziphus spina-christi (ZSC) tree, available abundantly in the Gulf region, was used to prepare CGAs to remove cationic and anionic dyes from aqueous media in a flotation column. Freshly prepared CGAs were used to remove cationic dye (methylene blue, MB) and/or anionic dye (Congo red, CR), resulting in concentrate and tailings. The concentrate solution was then collected and reused to generate new CGAs to remove oppositely charged dyes from the aqueous media. The maximum MB dye removal with the fresh CGAs was 79% at an initial concentration of 50 mg/L. Regenerated and reused CGAs achieved an additional 37% removal of CR. The synthetic anionic surfactant, sodium dodecyl benzenesulfonate (SDBS), was also used to prepare CGAs for the removal of mixed dyes (CR and MB). At pH 11, the dye removal was about 75% for MB and 88% for CR. Therefore, a one-step or two-step CGAs flotation process can potentially be used for the removal of single and mixed dyes.

Statistical modeling of phosphorus solubilization from chemical sludge and evaluation of optimal sodium hydroxide dose

Phosphorus (P) recovery from sludge has drawn widespread attention across the world to minimize the P load to the watershed, a concern for eutrophication, and to meet the stringent effluent discharge regulations in some countries. Waste activated sludge (WAS) and dewatered sludge (DS) were treated with a wide range of NaOH doses (0–0.75 g g−1 TS). The WAS sludge was diluted to 4.5%–2.25% of TS before the treatment to make comparable amount of TS as of DS (2.25%–1.5%). The kinetic study illustrated that P solubilization reached equilibrium within the first 20 min of treatment duration. Significant positive correlation was found between solution pH and P solubilization, whereas effect of TS was mostly insignificant. The experimental data was well fitted to the exponential models and exhibited maximum P solubilization of about 67% and 56% from the DS and WAS at NaOH doses of 0.71 and 0.27 g g−1 TS, respectively. The optimal NaOH application dose of 0.36 g g−1 TS for DS and 0.20 g g−1 TS for WAS were obtained with 64% and 48% of P solubilization, respectively. The modeling approach and the optimal dose of NaOH illustrated in this study could be utilized for other types of sludges having similar P to TS ratio and P solubilization mechanisms could be further extended to other type of P recovery techniques.

Regulatory costs on U.S. salmonid farms

The economic effects of the implementation of regulations on aquaculture farms in the United States, while of concern, are not well understood. A national survey was conducted of salmonid (trout and salmon) farms in 17 states of the United States to measure on‐farm regulatory costs and to identify which regulations were the most costly to this industry segment. The response rate was 63%, with a coverage rate of 94.5% of the U.S. production of salmonids. The regulatory system resulted in increased national on‐farm costs of $16.1 million/year, lost markets with a sales value of $7.1 million/year, lost production of $5.3 million/year, and thwarted expansion attempts estimated at $40.1 million/year. Mean farm regulatory costs were $150,506/farm annually, or $2.71/kg; lost markets with annual sales values of $66,274/farm; annual lost production of $49,064/farm; and an annual value of thwarted expansion attempts estimated at $375,459/farm. Smaller‐scale farms were affected to a disproportionately greater negative extent than larger‐scale farms. Per‐farm regulatory costs were, on average, greater for foodfish producers than for producers selling to recreational markets, but per‐kg regulatory costs were greater for those selling to recreational compared to foodfish markets. Regulatory costs constituted 12% of total production and marketing costs on U.S. salmonid farms. The greatest regulatory costs were found to be effluent discharge regulations. The majority of regulatory costs were fixed costs, but regulatory barriers to expansion precluded compensatory adjustments to the business in spite of growing demand for salmonid products. Results of this study show that the on‐farm regulatory cost burden is substantial and has negatively affected the U.S. salmonid industry's ability to respond to strong demand for U.S. farm‐raised salmonid products. Results also suggest that the regulatory system has contributed to the decline in the number of U.S. salmonid farms. While regulations will necessarily have some degree of cost to farms, the magnitude of the on‐farm regulatory cost burden on U.S. salmonid farms calls for concerted efforts to identify and implement innovative regulatory monitoring and compliance frameworks that reduce the on‐farm regulatory cost burden.

Vertical flow constructed wetland planted with Heliconia psittacorum used as decentralized post-treatment of anaerobic effluent in Southern Brazil

In order to investigate the potential of vertical flow constructed wetlands (VFCWs), a 24.5 m2 surface area filled with gravel and planted with Heliconia psittacorum, was implemented as an experimental system for domestic wastewater treatment in southern Brazil. The aims of the study were to (i) evaluate the performance of a full scale system septic tank (ST) and VFCW for decentralized domestic wastewater treatment, and (ii) identify the influence of Heliconia for hydraulic characteristics and consequent performance of the VFCW. The applied load rates in the VFCW were, on average, 10 g biochemical oxygen demand (BOD) m−2 day−1, 4 g NH4+-N m−2 day−1 and a hydraulic loading rate (HLR) of 60 mm day−1. Physicochemical analyses of wastewater treatment were carried out through grab sample methodology, for 5 months. Additionally, hydrodynamic tests were performed during plant development using rhodamine. The study demonstrated the viability of the system for decentralized wastewater treatment in Brazil, with average removal efficiencies of 78% for chemical oxygen demand (COD) and 84% for total suspended solids (TSS), according to national effluent discharge regulations. In spite of media’s large size, the VFCW achieved good average removal efficiencies. The tracer test results showed that the VFCW average hydraulic detention time increased as plants grew. This may have occurred due to interception of wastewater applied on the macrophyte’s leaves as well as a reduction in filter media permeability caused by the spread of roots and rhizomes. These results indicate that the plants played an important role in increasing wastewater contact time in wetlands with high hydraulic conductivity such as a gravel VFCW.

DOMESTIC WASTEWATER IN INDONESIA: CHALLENGE IN THE FUTURE RELATED TO NITROGEN CONTENT

The option of reusing treated wastewater is becoming necessary for environment sustainability approach. In fact, wastewater effluent discharge regulations have become stricter leading to a better water quality. Municipal activities, agriculture, and rapid urbanization led to increased nitrogen and phosphorus discharge to the water system. More often, the effluents from municipal wastewater treatment plant failed to meet the national standard for effluent quality. Excess nutrients, mostly N and P is the main cause of eutrophication the which results in oxygen depletion, biodiversity reduction, fish kills, odor, and increased toxicity. Biological nutrient removal technologies are preferred and widely used to remove nitrogen and phosphorus from domestic wastewater and protect water quality. Chemical compositions in wastewater are highly diverse substances from simple compounds to complex polymers. Some wastewater samples were analyzed in this research. Conventional technology still retains the basic principle of complete nitrogen cycle through nitrification and denitrification. Anammox is a sustainable and cost-effective alternative to the basic method of nitrogen removal. Anammox has been identified as a new biotechnology for nitrogen reduction from wastewater. Compared to the common process of nitrogen removal, anammox can reduce 64% offaeration, 100% of an exogenous electron donor, and sludge production by 80-90%. Some benefits from anammox include high nitrogen removal rate, lower operational cost, and small space requirements. Anaerobic baffled reactor (ABR) in Indonesia has been used commonly as communal wastewater treatment. Promoting anammox process in ABR potentially become an improvement for ABR in removing nitrogen better. This combination process still outlined for further research.

Estimating marginal abatement costs for industrial water pollution in Colombo

This paper estimates the cost of effluent discharge regulations for firms located in the lower Kelani River catchment in Sri Lanka. The river provides water for many economic purposes including drinking water to the capital city, Colombo and a variety of ecosystem services. Employing multi-input and multi-output translog production technology, we estimate shadow prices of effluents and technical efficiency of firms belonging to eight industries. With the given level of compliance, we extend our analysis to compute total abatement cost for firms under different policy scenarios, related to simultaneous reduction in concentration of three water pollutants including current regulatory standards. The evidence of poor compliance and wide variations in firm and industry specific shadow prices (marginal abatement costs) provide a strong case for a comprehensive redesign of environmental policy to control water pollution by industries in the heavily industrialized river catchment.

Modified reduced buoyancy flux model for desalination discharges

Large-scale desalination facilities are increasingly employed to supplement potable water supplies for many cities, where the demand for water is having a negative impact on the sustainability of natural water resources. A primary environmental concern with the establishment of these large-scale facilities is the effective disposal of the hyper-saline effluent brine, so that harmful effects on the marine environment are minimised. In countries with effective effluent discharge regulations, the negatively buoyant brine is typically released through submerged diffusers, where the ports are inclined towards the ocean surface to aid dispersion processes. Predictive models provide an inexpensive method of considering different sources and ambient design parameters. It has been demonstrated that predictive models developed primarily for positively buoyant discharges significantly underestimate dilution measured by physical studies, when applied to negatively buoyant desalination discharges. It has been shown recently that predicted dilution and geometric parameters can be improved if a reduction in the buoyancy flux of the main flow is incorporated into these models. Here, the reduced buoyancy flux (RBF) approach is modified through the use of a physically based buoyancy loss mechanism. Improvements in the predictive capabilities of the new model are demonstrated through comparisons with predictions from existing models and an extensive range of results from physical studies for geometric, dilution, and velocity parameters.

Treatment of contaminated soil leachate by precipitation, adsorption and ion exchange

The alkaline washing of soil polluted by organic (pentachlorophenol (PCP) and polychlorinated dioxins and furans (DF)) and inorganic (As, Cr, and Cu) compounds generates large volumes of effluents with high concentrations of contaminants. The objective of the present study is the treatment of leachate produced by a soil decontamination process under alkaline conditions. The alkaline leachate (pH0 13.1) initially contains [As]0=14.5mgL−1, [Cr]0=2.41mgL−1, [Cu]0=8.22mgL−1, [PCP]0=6.42mgL−1 and [DF]0=127ng TEFL−1. Precipitation allows the reduction of the concentrations to below 5mg/L for Cu and below 1mg/L for PCP and As to comply with regulations for effluent discharge in sewer in Quebec City and Montreal. The concentration of Cr was taken into consideration in this study even if it is below the legal limit (5mg/L) without any treatment. Precipitation is the most efficient technique investigated here for the simultaneous removal of metals and PCP but does not eliminate DF beyond 17%. None of the activated carbons and resins tested can effectively remove As and Cr in strong alkaline media. The anionic resin Lewatit SR7 developed for anion exchange in strong alkaline media is the most effective for the simultaneous removal of Cu, PCP and DF, with recovery yields of 83, 99 and 97%, respectively.

Demonstration of the efficiency and robustness of an acid leaching process to remove metals from various CCA-treated wood samples

In recent years, an efficient and economically attractive leaching process has been developed to remove metals from copper-based treated wood wastes. This study explored the applicability of this leaching process using chromated copper arsenate (CCA) treated wood samples with different initial metal loading and elapsed time between wood preservation treatment and remediation. The sulfuric acid leaching process resulted in the solubilization of more than 87% of the As, 70% of the Cr, and 76% of the Cu from CCA-chips and in the solubilization of more than 96% of the As, 78% of the Cr and 91% of the Cu from CCA-sawdust. The results showed that the performance of this leaching process might be influenced by the initial metal loading of the treated wood wastes and the elapsed time between preservation treatment and remediation. The effluents generated during the leaching steps were treated by precipitation–coagulation to satisfy the regulations for effluent discharge in municipal sewers. Precipitation using ferric chloride and sodium hydroxide was highly efficient, removing more than 99% of the As, Cr, and Cu. It appears that this leaching process can be successfully applied to remove metals from different CCA-treated wood samples and then from the effluents.

Environmental performance of biological nutrient removal processes from a life cycle perspective

The goal of the present study is to assess different alternatives for a wastewater treatment plant module with capacity to remove nutrients biologically, taking into account present Argentine regulations for effluent discharge. A computational modeling tool (GPS-X) was employed to simulate the behavior of the different alternatives, and Life Cycle Assessment was applied to quantify the environmental impact. A 2000 m(3)/d municipal wastewater flow was used to carry out the simulations, the annual flow was utilized as functional units and the main topics analyzed were energy efficiency, land use, eutrophication reduction and biosolid reuse. Biogas and biosolid generation was evaluated as a good opportunity to generate a cleaner process. This study highlights the fact that nutrient removal processes significantly improve the quality of effluent and biosolids and reduces energy consumption.

Algal Uptake of Hydrophobic and Hydrophilic Dissolved Organic Nitrogen in Effluent from Biological Nutrient Removal Municipal Wastewater Treatment Systems

Dissolved organic nitrogen (DON) accounts for a large fraction of the total nitrogen discharged to surface waters by municipal wastewater treatment plants designed for biological nutrient removal (BNR). Previous research indicates that some but not all of the DON in wastewater effluent is available to bacteria and algae over time scales that are relevant to rivers and estuaries. To separate bioavailable DON from nitrate and less reactive DON species, an XAD-8 resin coupled with an anion exchange treatment was employed prior to chemical analysis and algal bioassays. Analysis of effluent samples from a range of municipal BNR plants (total DON concentrations ranging from 0.7 to 1.8 mg N/L) employing a range of technologies indicated that hydrophilic DON, which typically accounted for approximately 80% of the total DON, stimulated algal growth, whereas hydrophobic DON, which accounted for the remaining DON, remained at nearly constant concentrations and had little or no effect on algal growth during a 14-day incubation period. The hydrophobic DON exhibits characteristics of humic substances, and is likely to persist for long periods in the aquatic environment. The distinct differences between these two classes of DON may provide a basis for considering them separately in water quality models and effluent discharge regulations.

Design and performance of a pilot-scale equipment for CCA-treated wood remediation

Increasingly stringent regulations regarding waste disposal encourage the development of options for reuse, recycling and revalorisation of waste. Metals-bearing treated wood wastes are no exception. Previous studies identified a possible treatment technology for chromated copper arsenate (CCA) preservative-treated wood waste based on sulphuric acid leaching. In this study, the scale-up of this technology was extended from 200 ml flask to 80 l working volume stirred-tank reactor. The study involved three leaching steps of 2 h each, at 75 °C with 0.2 N H 2SO 4 and 15% solids content followed by three rinsing steps. This procedure led to removal of 99.5% of the arsenic, 95.7% of the chromium and 99.6% of the copper from the wood chips on average. The effluents generated by the leaching steps were then treated by precipitation. This technology allowed 99% removal of As, Cr and Cu from the leachate, leading to effluents satisfying the regulations for effluent discharge in municipal sewers. The mass balance was assessed for the whole process (leaching, rinsing and precipitation of the leachate) and the output to input ratio was between 80% and 100%. Furthermore, the economic analysis concluded that the operating cost of the process (leaching, rinsing and precipitation of the leachate) was about 250 $/ton of treated wood (t.t.w.) with the conditions employed in this study. However, the cost could be reduced at least to 89 $/t.t.w. by using a counter current leaching process as developed in a previous study.

Removal of metal from acid mine drainage (AMD) by using natural zeolite of Nizarneshwar Hills of Western India

The mining industry faces stringent effluent discharge regulations and has acknowledged that it is necessary to look into innovative technologies to recycle considerable amount of effluent rather than discharging into surface water. Effluents from mines give rise to aesthetic unpleasantness. The focus of the investigations was to cope with more stringent effluent discharge regulations and to protect the ecosystem from harmful pollutants in the mine effluents. Copper is one of the heavy metal in the mine systems, which are known to be a harmful element. The present study has been undertaken to investigate a process that might remove Cu(II) from mine waste water by using natural zeolite, such as stilbite, and compared with synthetic resins like CSA-9 and CSA-609D. In this study, natural zeolite was used as a low-cost adsorbent to evaluate its ability to remove heavy metals from acid mine drainage. The zeolite used in this study is the natural clay mineral from the Nizarneshwar Hills of Western India. Three resins tested are CSA-9, natural zeolite–stilbite, and CSA-609D. Batch testing has been conducted to select effective ion-exchange resins for copper removal and to determine effective regenerants for regeneration of exhausted resins. All tests were conducted at bench scale and in batch mode. Three strong acid cation exchangers were evaluated to compare their metal removal capacities. The metal concentration in the effluent was reduced with all resins tested. It was found that, among all the three types of natural zeolite, stilbite shows the highest removal efficiency of copper in every parameter that is considered for evaluating the performance of resins.

Activated sludge versus aerated lagoon treatment of kraft mill effluents containing β-sitosterol and stigmasterol

In the present study the performance of an activated sludge system (AS) and an aerated lagoon (AL) are compared for the treatment of kraft cellulose effluents. Both reactors were operated at organic loading rates (OLR) up to 9 g COD/L· d. The activated sludge system presented better performance at high OLR than the aerated lagoon with removal percentages of 57–67% and 95% of COD and BOD5, respectively. The removal percentages of specific compounds were always slightly higher in the case of the AS than in the AL with exception of the total phenolic compounds which concentration increased in the former. Furthermore the analyzed fractions from the effluents indicated that in the AS the compounds were fully removed while in the case of the aerated lagoon were transformed into compound with low molecular weight P2 (5 kD < MW < 10 kD). In the case of the AS system the increase of the total phenolic compounds concentrations was corroborated with the increase of the fractions P2, P3 and P4. The studied phytosterol were removed from the effluent at concentrations up to 2 mg/L in percentages close to 100% mainly by adsorption in the case of the AL and by a combining adsorption and mainly degradation in the AS. The BOD5 concentration in the effluent of both systems fulfilled the requirements of the Chilean regulations for effluent discharge indicating the feasibility of aerobic treatment of this kind of effluents.

Performance evaluation of a simple wastewater treatment system comprised by UASB reactor, shallow polishing ponds and coarse rock filter

The work investigates a small full-scale wastewater treatment system comprised by the following units in series: UASB reactor, three polishing ponds and one coarse rock filter. The overall performance of the system is analyzed based on three years of monitoring using physical-chemical and biological parameters. Good organic matter, suspended solids and ammonia removal is achieved, together with excellent coliform removal (5.70 log units). Mean effluent concentrations of the main parameters are: BOD: 39 mg/L; COD: 109 mg/L; SS = 41 mg/L; ammonia: 10 mg/L; E. coli: 540 MPN/100 mL, indicating compliance with many regulations for effluent discharge and reuse. Main algal classes found in the ponds and final effluent were chlorophyta and euglenophyta. The system is completely unmechanized and has a relatively small total hydraulic retention time (less than 13 days), compared with most natural treatment processes. No sludge removal from the ponds and filter has been necessary so far.

Reducing phosphorous discharge from flow-through aquaculture: II: Hinged and moving baffles to improve waste transport

In many flow-through (FT) raceway facilities, low raceway water current velocities lead to the settlement of solid wastes in raceway rearing areas and subsequent inadequate transport from the rearing areas to quiescent zones (q-zones). Such facilities must employ regular manual labor to sweep raceways of the settled wastes in order to aid compliance with effluent discharge regulations. Two new baffle configurations, a hinged and a moving system, have been designed to address these limitations and improve waste transport in the rearing areas of FT raceways. The effect of the baffles on channel velocities, transport rates, and transport efficiencies was tested during pilot and commercial scale tests. The results showed average under baffle velocities during commercial tests of 0.28 and 0.40m/s for the hinged and moving baffle configurations, respectively. These values are within recommended velocity ranges for salmonid waste transport in FT raceways, and are an order of magnitude higher than the comparable velocities measured during control tests. Pilot scale tests showed average transport rates of 5.87, 3.09, and 0.04g simulated waste/min for hinged and moving baffles, and control, respectively. Measured transport efficiencies of input simulated waste during commercial tests were 75, 55, and 15% for the moving and hinged baffles, and control, respectively. Of the two tested designs, the moving baffle is most suitable for commercial use given the simplicity of the single baffle design and the test results. Although the operational parameters and design refinements will vary by facility, the moving baffle concept has application as a simple and effective solid waste transport improvement.