Removal Efficiency Of Suspended Solids Research Articles

Physico-chemical and bacteriological characterization of wastewater from Mexico City

This study was designed to characterize the behavior of the wastewater produced by Mexico City after being subjected to a physico-chemical treatment of Al2(SO4)3 and FeCl3 in a jar test simulation of an Advanced Primary Treatment (APT). Special attention was paid to the evaluation of the removal efficiency of suspended solids and of helminth eggs. The effluent thus obtained was first subjected to a simulated filtration process (through a fiberglass filter paper with an opening of 11 μm) and then it was disinfected with the use of two chemicals: sodium hypochlorite (NaOCl) and copper sulphate (CuSO4). The use of both the Al2(SO4)3 (dose ranging from 25 to 40 mg/L) and the FeCl3 (varying from 20 to 40 mg/L) in combination with the filtration process proved to be quite effective in what refers to the removal mechanisms of helminth eggs. The concentrations recorded in each of the effluents fell always below the international regulations for irrigation reuse (<1 org/L as helminth eggs). The removal rates achieved for both coagulants were close to 99%. In what refers to the disinfection accomplished with the use of NaOCl (from 4 to 17 mg/L as Cl2) and CuSO4 (from 3 to 5 mg/L as Cu), it was found to be an excellent supplementary process because less than 1000 CFU/100 mL were recorded and this value satisfies the international recommendations. The treatment as a whole showed removal efficiencies of 45% as COD, 73% SST, 99% helminth eggs, 99.99% faecal coliforms and from 7 to 87% in heavy metals.

Anaerobic digestion of primary sludge from chemical pre-precipitation

Many existing wastewater treatment plants are to be upgraded for phosphorus removal. In our study, ferric chloride was used as a coagulant in pre-precipitation of municipal sewage. Using a Fe/P molar ratio of 0.8, removal efficiencies for suspended solids (64%), chemical oxygen demand (50%), Kjeldahl nitrogen (22%), total phosphorus (43%) and orthophosphate (51%) were obtained. Anaerobic digestion of raw primary sludge yielded a volatile solids (VS) destruction of 35% at VS loading rates of 0.60 to 0.79 kg VS/m3.d. Digestion of chemically enriched primary sludge (CEP-sludge) yielded a VS destruction of 57% at a VS loading rate of 1.36 kgVS/m3.d. Comparison of the methane production per kg VS destroyed (519 to 612 1 CH4/kgVS destroyed for primary sludge, 299 to 395 1 CH4/kgVS destroyed for CEP-sludge) evidenced a change in the composition of the organic material after precipitation with coagulants; the latter sludge was enriched in less reduced compounds. The precipitated phosphorus was not released to the supernatant during anaerobic digestion. No evidence for reduced digester stability was found for digestion of CEP-sludge. These results indicate that retro-fitting a plant by chemical pre-precipitation and subsequent anaerobic digestion of the CEP-sludge is a feasible option.

Water treatment and waste characterization evaluation of an intensive recirculating fish production system

A combination of two different technologies used for fish production was evaluated at the North Carolina State University (NCSU) F̀ish Barn facility. The combined system included the ECOFISH∗ tank, developed at the Norwegian Hydrotechnical Laboratory (NHL) at SINTEF (Trondheim, Norway) and water treatment and recycle technology designed at NCSU. Approximately 2170 fingerling tilapia ( Oreochromis niloticus, Oreochromis niloticus × Oreochromis aureus) were grown from 3.6 to 507 g in 177 days in a 20 m 3 four-zone tank. The system design included patented particle traps at the bottom of each zone to remove feed waste and excrement, sludge collectors where the removed particles settled, a rotating screen filter for suspended solids removal, a high-rate linear-path trickling biological filter for nitrification, and two down-flow columns for oxygen injection. The measured suspended solids level in the tank zones were usually less than 7.5 mg l −1. Based on six efficiency tests with a mean total ammonia nitrogen (TAN) concentration in the culture tank of 0.62 mg l −1, the biofilter removed approximately 65% on a single pass through the filter, with an average removal rate per unit of filter surface area of 0.33 g TAN m −2 day −1. Sampling every 4 h over a 24-h period showed variability in concentrations and TAN removal rates by the biofilter. Six efficiency tests on the sludge collectors and the screen filter showed 80% and 41% suspended solids removal efficiency, respectively, based on the influent and effluent concentrations. On a daily basis, the sludge collectors and the screen filter each removed about 18% of feed volatile solids input, respectively, based on three 24-h periods studied. Fresh water use averaged approximately 1500 l day −1, which was about 7% of the system volume.

Anaerobic digestion of primary sludge from chemical pre-precipitation

Many existing wastewater treatment plants are to be upgraded for phosphorus removal. In our study, ferric chloride was used as a coagulant in pre-precipitation of municipal sewage. Using a FeIP molar ratio of 0.8, removal efficiencies for suspended solids (64%), chemical oxygen demand (50%), Kjeldahl nitrogen (22%), total phosphorus (43%) and orthophosphate (51 %) were obtained. Anaerobic digestion of raw primary sludge yielded a volatile solids (VS) destruction of 35% at VS loading rates of 0.60 to 0.79 kg VS/m3.d. Digestion of chemically enriched primary sludge (CEP-sludge) yielded a VS destruction of 57% at a VS loading rate of 1.36 kgVS/m3.d. Comparison of the methane production per kg VS destroyed (519 to 612 1 CH4/kgVS destroyed for primary sludge, 299 to 395 1 CH4/kgVS destroyed for CEP-sludge) evidenced a change in the composition of the organic material after precipitation with coagulants; the latter sludge was enriched in less reduced compounds. The precipitated phosphorus was not released to the supernatant during anaerobic digestion. No evidence for reduced digester stability was found for digestion of CEP-sludge. These results indicate that retro-fitting a plant by chemical pre-precipitation and subsequent anaerobic digestion of the CEP-sludge is a feasible option.

Technical note

An analysis of the performance of primary clarifiers at the Regina Wastewater Treatment Plant was undertaken based on the average monthly operational data from 1981 to 1990. Removal efficiencies of suspended solids (SS) and biochemical oxygen demand (BOD) in the wastewater were related to surface overflow rate of clarifiers and influent concentration of SS and BOD respectively in a mathematical model.

Removal of solids, nitrogen, and phosphorus in the Cache River wetland

Mass flux measurements collected between April 1987 and September 1990 at the upstream and downstream boundaries of the Cache River Wetland (CRW), a bottomland hardwoof forest in eastern Arkansas, were used to estimate long-term, average removal efficiencies (RE, %) for inorganic suspended solids (ISS), total nitrogen (TN), and total phosphorus (TP). The observed removal efficiencies were used with a steady-state, first-order removal model to compute removal rate constant. Detention time of the CRW was determined with a time-varying, two-dimensional, depth-averaged, numerical flow and transport model. The computed average detention time of 5.02 da was close to the average hydraulic retention time of 5.15 da, justifying the plug flow assumption of the model. The removal rate constants estimated from the CRW data for ISS, TN, and TP were 0.066 m/da, 0.048 da−1, and 0.0058 m/da (2.1 m/yr), respectively. The denitrification rate constant estimated for the CRW was 0.24 da−1. These rate constants are in general agreement with values obtained from the literature.

Tube settling of high-rate pond algae

The effluent of a high-rate pond (HRP) may contain 200 to 400 mg/L of algal suspended solids (SS). Microalgae must be separated before the effluent is discharged. Gravity sedimentation is usually the first method considered in algal wastewater treatment systems. However, required overflow rates (OFRs) to remove algae in the conventional clarifiers are too low. Therefore, the shallow-depth sedimentation concept was studied for the separation of Micractinium from HRP effluent in order to increase the OFRs of gravity settling equipment. Using the orthogonal squares experimental plan, the design parameters, such as OFR, tube diameter, tube length, and inclination, were evaluated for algal SS removal. A circular upflow clarifier was run as a control. At an OFR of 8.15 L/m2 · min (0.2 gpm/ft2), SS removal efficiencies of tube settling and upflow clarifier were 80% and 18%, respectively. When the OFR was increased to 16.3 L/m2 · min (0.4 gpm/ft2), SS removal efficiencies decreased to 61% in tube settler and to 11% in upflow clarifier. SS removal efficiencies of tube settlers were 40% at 30.6 L/m2 · min (0.75 gpm/ft2) and 20% at 71.3 L/m2 · min (1.75 gpm/ft2). A linear relationship exists between removal efficiency and the diameter and length of tubes. The relationship is parabolic for the inclination of tubes and the OFR. The overall algae removal efficiency increased with the tube length but it was an inverse function of OFR, tube diameter, and inclination. At an OFR of 12.2 L/m2 · min (0.3 gpm/ft2), algae removal efficiencies were 7 to 8 times better than that of upflow clarifier. It was demonstrated that OFR in a gravity settler could be increased 4 to 5 times using tube settlers.

Tube settling of high-rate pond algae

The effluent of a high-rate pond (HRP) may contain 200 to 400 mg/L of algal suspended solids (SS). Microalgae must be separated before the effluent is discharged. Gravity sedimentation is usually the first method considered in algal wastewater treatment systems. However, required overflow rates (OFRs) to remove algae in the conventional clarifiers are too low. Therefore, the shallow-depth sedimentation concept was studied for the separation of Micractinium from HRP effluent in order to increase the OFRs of gravity settling equipment. Using the orthogonal squares experimental plan, the design parameters, such as OFR, tube diameter, tube length, and inclination, were evaluated for algal SS removal. A circular upflow clarifier was run as a control. At an OFR of 8.15 L/m2 . min (0.2 gpm/ft2), SS removal efficiencies of tube settling and upflow clarifier were 80% and 18%, respectively. When the OFR was increased to 16.3 L/m2 · min (0.4 gpm/ft2), SS removal efficiencies decreased to 61% in tube settler and to I 1% in upflow clarifier. SS removal efficiencies of tube settlers were 40% at 30.6 L/m2 . min (0.7S gpm/ft2) and 20% at 71.3 L/m2 · min (1.7S gpm/ft2). A linear relationship exists between removal efficiency and the diameter and length of tubes. The relationship is parabolic for the inclination of tubes and the OFR. The overall algae removal efficiency increased with the tube length but it was an inverse function of OFR, tube diameter, and inclination. At an OFR of 12.2 L/m2 · min (0.3 gptn/ft2), algae removal efficiencies were 7 to 8 times better than that of upflow clarifier. It was demonstrated that OFR in a gravity settler could be increased 4 to 5 times using tube settlers.

Evaluation of daqahla wastewater treatment plant, aerated lagoon and ponds system

In Egypt, Daqahla wastewater treatment plant (WTP) includes two anaerobic ponds, one aerated lagoon followed by three maturation ponds. It started operation in 1989. This plant is chosen as an example for evaluation as a cost-effective method for wastewater treatment in rural areas. A sanitary survey, laboratory analysis and cost survey were carried out during the period between December 1991 to September 1992. It was found that Daqahla community has high strength wastewater characterised by an average BOD5 of 454 mg/l and average SS of 508 mg/l. Furthermore, it was noticed that Daqahla WTP was loaded with an actual flow (833 m3/d) higher than the design flow (520 m3/d). In addition there was a wide fluctuation in the loads applied to the system. The system was evaluated, and the average removal efficiencies of suspended solids, BOD5 and COD were 92%, 95% and 93% respectively. While there was no removal of ammonia and phosphate, with respect to the efficiency of the anaerobic ponds, it was noticed that about 50% of the organic loading was removed and this is consistent with the literature. In order to upgrade the efficiency of the aerated lagoon and the first maturation pond, the design load and detention time must be taken into consideration. Sludge removal processes must be considered since the first maturation ponds was working as a settling pond. It was noticed that the second and the third maturation ponds were working as facultative ponds. To upgrade their efficiencies, the actual organic loading must not exceed the design load with a minimum retention time of 3 days per pond. The cost survey indicates that the construction cost is 63 LE/cap. Land costs in delta and desert areas are 19 and 2 LE/cap., respectively (acre prices in delta and desert are 40000 and 4000 LE respectively. Total construction cost in the delta is 82 LE/cap., while in the desert, the total construction cost is 65 LE/cap. Furthermore, the operation and maintenance cost is 12 LE/cap. year.

Modelling the performance of anaerobic wastewater stabilization ponds

The performance of the primary anaerobic pond at the Alsamra Wastewater Treatment Plant in Jordan was monitored over 48 months. Overall averages for the removal efficiencies of BOD5, COD and suspended solids were 53%, 53% and 74%, respectively. An improvement in removal efficiency with increase in pond water temperature was demonstrated. A model, which takes into account the variability of raw wastewater at different locations, has been developed to describe the performance of a primary anaerobic pond in terms of a settleability ratio for the raw wastewater. The model has been verified by illustrating the high correlation between actual and predicted pond performance.

Municipal wastewater treatment by lime/ferrous sulfate and dissolved air flotation

In this work a chemical treatment system for municipal wastewater using copper cementation effluent and lime as coagulants in combination with dissolved air flotation, was investigated. Copper cementation effluent (CCE) containing about 45% dissolved solids (density=1.31) is a liquid waste from a leaching process, which is disposed in large ponds by several copper mines in the North of Chile. CCE contains a combination of ferrous iron, sulfate, chlorine, magnesium, sodium, residual copper and other ions. For its use as a coagulant, CCE was treated using a low cost process. Ferric hydroxide flocs precipitated after CCE addition were efficiently removed by dissolved air flotation producing a low density froth. High suspended solid removal efficiency, process flexibility, short overall residence time in addition to low cost of chemicals used and precipitation of varied proportions of contaminants, including bacteria from wastewater, are the main features of this chemical treatment system.

Evaluation of Daqahla wastewater treatment plant, aerated lagoon and ponds system

In Egypt, Daqahla wastewater treatment plant (WTP) includes two anaerobic ponds, one aerated lagoon followed by three maturation ponds. It started operation in 1989. This plant is chosen as an example for evaluation as a cost-effective method for wastewater treatment in rural areas.A sanitary survey, laboratory analysis and cost survey were carried out during the period between December 1991 to September 1992. It was found that Daqahla community has high strength wastewater characterised by an average BOD5 of 454 mg/l and average SS of 508 mg/l. Furthermore, it was noticed that Daqahla WTP was loaded with an actual flow (833 m3/d) higher than the design flow (520 m3/d). In addition there was a wide fluctuation in the loads applied to the system. The system was evaluated, and the average removal efficiencies of suspended solids, BOD5 and COD were 92%, 95% and 93% respectively. While there was no removal of ammonia and phosphate, with respect to the efficiency of the anaerobic ponds, it was noticed that about 50% of the organic loading was removed and this is consistent with the literature. In order to upgrade the efficiency of the aerated lagoon and the first maturation pond, the design load and detention time must be taken into consideration. Sludge removal processes must be considered since the first maturation ponds was working as a settling pond. It was noticed that the second and the third maturation ponds were working as facultative ponds. To upgrade their efficiencies, the actual organic loading must not exceed the design load with a minimum retention time of 3 days per pond.The cost survey indicates that the construction cost is 63 LE/cap. Land costs in delta and desert areas are 19 and 2 LE/cap., respectively (acre prices in delta and desert are 40000 and 4000 LE respectively). Total construction cost in the delta is 82 LE/cap., while in the desert, the total construction cost is 65 LE/cap. Furthermore, the operation and maintenance cost is 12 LE/cap.year.

Modelling the performance of anaerobic wastewater stabilization ponds

The performance of the primary anaerobic pond at the Alsamra Wastewater Treatment Plant in Jordan was monitored over 48 months. Overall averages for the removal efficiencies of BOD5, COD and suspended solids were 53%, 53% and 74%, respectively. An improvement in removal efficiency with increase in pond water temperature was demonstrated. A model, which takes into account the variability of raw wastewater at different locations, has been developed to describe the performance of a primary anaerobic pond in terms of a settleabthty ratio for the raw wastewater. The model has been verified by illustrating the high correlation between actual and predicted pond performance.

Municipal wastewater treatment by lime/ferrous sulfate and dissolved air flotation

In this work a chemical treatment system for municipal wastewater using copper cementation effluent and lime as coagulants in combination with dissolved air flotation, was investigated. Copper cementation effluent (CCE) containing about 45% dissolved solids (density = 1.31) is a liquid waste from a leaching process, which is disposed in large ponds by several copper mines in the North of Chile. CCE contains a combination of ferrous iron, sulfate, chlorine, magnesium, sodium, residual copper and other ions. For its use as a coagulant, CCE was treated using a low cost process. Ferric hydroxide floes precipitated after CCE addition were efficiently removed by dissolved air flotation producing a low density froth. High suspended solid removal efficiency, process flexibility, short overall residence time in addition to low cost of chemicals used and precipitation of varied proportions of contaminants, including bacteria from wastewater, are the main features of this chemical treatment system.

An anaerobic fluidized pellet bed bioreactor process for simultaneous removal of organic, nitrogenous and phosphorus substances

A new wastewater treatment process, which is named herein “the anaerobic fluidized pellet bed (AFPB) bioreactor process”, is developed for simultaneous removal of suspended solids, organic matter, phosphorus and nitrogen. This process is composed of two stages: an upflow AFPB bioreactor for the first stage and an activated sludge aeration tank with a sludge settling zone for the second stage. The first stage, the AFPB bioreactor, is introduced as an alternative to the primary clarifier. In this stage, polymerized aluminum chloride and a weak anionic polymer are dosed in order to coagulate suspended solids, colloidal matters and phosphorus and to generate sludge pellets that are large enough to settle rapidly. The excess sludge pellets are withdrawn from the bottom of the AFPB bioreactor. The second stage is primarily designed for the usual aerobic biological treatment of organic matter. In addition, as the aeration tank is operated at solid retention times long enough to ensure the growth of nitrifiers even at temperatures below 10°C, high nitrification is achieved in the second stage. The nitrified effluent is recycled from the second stage to the AFPB bioreactor, and denitrification completely accomplished under the anaerobic conditions. The organic matter necessary for the denitrification is supplied through anaerobic biological hydrolysis of the sludge pellets in the AFPB bioreactor. With a total retention time of 4 h (2 h in the AFPB bioreactor and 2 h in the aeration tank) and a recirculation ratio of 300% based on the influent flow rate, the average removal efficiencies of suspended solids, total COD and total nitrogen are found to be 99, 95 and 75%, respectively. Total phosphorus was below the detectable level in most cases.

Sediment accumulation in detention or retention ponds

Accumulation of bottom sediments in nine highway wet detention ponds in central to south Florida were investigated. Sediment core samples were collected at each pond and were later analyzed in the laboratory. In-situ measurements of accumulated loose sediment depths above the parent soil in each pond were recorded. Existing models were used to calculate removal efficiency of suspended solids and to estimate the depth of accumulated sediments in each pond. Attempts were made to correlate measured and calculated sediment accumulation rates and the surrounding drainage area.

Continuous‐backwash upflow filtration for primary effluent

ABSTRACT: The objective of the research was to investigate the feasibility of continuous‐backwash upflow filtration of primary effluent. Feasibility was assessed on the basis of removal of suspended solids, turbidity, biochemical oxygen demand, and the change in particle size distribution over varying filtration rates. Continuous‐backwash filtration was effective over a wide range of wastewater filtration rates varying from 96 to 264 L/m2 · min (2.4 to 6.6 gal/ft2 · min). An average of 70% of the suspended solids (over an influent range from 8 to 56 mg/L), 46% of the turbidity (over an influent range from 20 to 72 NTU), and 27% of the total 5‐day biochemical oxygen demand (over an influent range from 61 to 101 mg/L) was removed by primary effluent filtration with no subsequent buildup of headloss. Neither the filtration rate nor the influent concentration influenced the removal efficiency for suspended solids, turbidity, biochemical oxygen demand, or affected the particle size distribution of the filtered effluent within the range evaluated.

Sludge removal from salmonid tank effluent using rotating microsieves

Effluent from tanks stocked with adult Atlantic salmon was treated using a UNIK Rotary Filter (URF) with submersed microsieves with screen mesh sizes of 350 to 60 μm. The mean removal efficiency of suspended solids and total phosphorus was 63–68%. Using a standard backwashing system the URF normally produces 10–20 litres of sludge water per m 3 treated tank effluent. By running the URF with vacuum suction equipment a reduction to about 0·3 litre of sludge water per m 3 tank effluent is possible. By using a two-step mechanical dewatering system which includes microsieving and sedimentation (UNIK), it was possible to achieve a further concentration in the order of 200–5000 times. This system produced daily a sedimented sludge volume of 1–1·5 litre/kg feed supplied (FCR c. 1·2 kg feed/kg fish produced). The dry matter content of the sludge was as high as 50–100 g/litre.

Performance Evaluation of Compact RBC-Settling Tank System

A laboratory study was conducted to investigate the performance of RBC-Settling tank system on wastewater treatment in comparison with conventional RBC. The same synthetic wastewater was fed parallel into four stage laboratory scale cascade-connected RBC-Settling tank and conventional RBC reactors at a fixed rotational speed and hydraulic loading. At three different organic loading rates of 6.14, 13.44 and 23.31 g SCOD/m2/day, the results of the systems are presented in terms of ammonia nitrogen (NH3-N), total kjeldahl nitrogen (TKN), organic and suspended solids (SS) loading and removal. Disk Biomass Index (DBI), Sludge Biomass Index (SBI) and Fractional Biomass Volatile Solids Destruction (FBVSD) were used to compare the disk active biomass and sludge stability of the RBC-Settling tank system with those of the conventional RBC. Removal efficiency of suspended solids, ammonia nitrogen and total Kjeldahl nitrogen was found to be much higher in the RBC-Settling tank system than the conventional RBC but organic removal in terms of SCOD removed g/m2/day of both reactors was not much different. Much better sludge stabilization was observed in the RBC-Settling tank system. The RBC-Settling tank system showed good performance on the suspended solids, NH3-N and TKN removal, and sludge stabilization as well as organic removal, which indicates that this is an effective and economical system for treating domestic wastewater in small and isolated communities.

Biological Treatment of Soya Bean Waste

Soya bean beverages and “Tofu” are the major sources of protein in the Asian diet. Wastewater from soya bean food processing plant consisted of high concentration of BOD5, COD, nitrogen and phosphorus. The wastewater should be pre-treated before discharging into the sewer or watercourses. Activated sludge process was an effective biological treatment process for soya bean wastewater. Up to 95% of BOD5 can be removed by activated sludge orocess. The removal of nitrogen and phosphorus were 67% and 57% respectively. The treatment efficiency increased with higher mean cell residence time. The settleability of activated sludge was good, and suspended solids removal efficiency was well above 90%. The biological kinetic coefficients were also determined from the pilot study.