Chemically Enhanced Primary Treatment Research Articles

Chemically enhanced primary treatment (CEPT) for removal of carbon and nutrients from municipal wastewater treatment plants: a case study of Shanghai

With Chemically Enhanced Primary Treatment (CEPT) as the short-term process, the capacity of Bailonggang Wastewater Treatment Plant accounts for almost 25% of the total capacity of wastewater treatment in Shanghai, China. However, shortly after this plant was placed in operation in 2004, it was found that the effluent of CEPT couldn't meet the new national discharge criteria. Although the removal of phosphate is almost 80%, chemical oxygen demand (COD) and ammonia nitrogen (NH3-N) in the effluent is frequently found to exceed the standards. The primary goal of this research is to investigate the possibility of optimizing the CEPT to make it meet the discharge criteria before it is upgraded to a secondary treatment. An oxidant is adopted to remove NH3-N, and a high performance polyaluminum chloride (HP-PACl) is synthesized to enhance the removal of COD. It is found that HP-PACl improves the removal of COD, and the oxidant enhances NH3-N removal effectively. However, to meet the requirement of a newly implemented stricter discharge standard, it is necessary to upgrade this CEPT to a secondary treatment. The results of this study provide scientific evidence for the upgrade of the Bailonggang Wastewater Treatment Plant.

Ferric coagulant recovered from coagulation sludge and its recycle in chemically enhanced primary treatment

An investigation was conducted to study the feasibility of ferric coagulant recovery from chemical sludge and its recycle in chemically enhanced primary treatment (CEPT) to make the process more cost-effective, as well as reduce sludge volume. The optimum conditions and efficiency of the acidification for ferric coagulant recovery from coagulation sludge were investigated. Experimental results showed that the recovered coagulants can be used in CEPT and the pollutants removal efficiency is similar to that of fresh coagulant, and for some aspects the effect of recovered coagulants is better than that of fresh ones, such as turbidity removal. Although some substances will be enriched during recycle, they have little effect on treated wastewater quality. Acidification condition also had significant influence on reduction of sludge volume. The efficiency of coagulant recovery had a linear relationship with sludge reduction. Experiments verify that it would be a sustainable and cost-effective way to recover ferric coagulant from coagulation sludge in water treatment and chemical wastewater treatment, and then recycle it to CEPT, as well as reduce sludge volume.

The Use of Chemically Enhanced Primary Treatment (CEPT) in Honduran Imhoff Tanks

The Use of Chemically Enhanced Primary Treatment (CEPT) in Honduran Imhoff Tanks

Definition of a practical multi-criteria procedure for selecting the best coagulant in a chemically assisted primary sedimentation process for the treatment of urban wastewater

Chemically assisted primary sedimentation (CAPS) or chemically enhanced primary treatment (CEPT) consists of adding chemicals in order to increase the coagulation, flocculation and sedimentation of raw wastewater. Over the last twenty years, the use of CAPS has increased due to the development of better coagulants and flocculation enhancers, stricter standards as well as the need for low-energy treatment technologies, especially in developing countries. This paper defines a very simple multi-criteria procedure to be used in order to select the best combination of coagulant and dose when using jar tests. It is based on the adoption of the following 5 criteria: COD percentage removal, sludge volume after 2 h, coagulant dose, coagulant cost, pH percentage variation. The mathematical affordability of the procedure was tested by comparing it with the well known analytic hierarchy process.

Characterization and treatability studies of tannery wastewater using chemically enhanced primary treatment (CEPT)—A case study of Saddiq Leather Works

Chemically enhanced primary treatment (CEPT) is a technology that uses coagulants for enhanced pollutants removal at the primary stage of the wastewater treatment. This paper presents the detailed characteristics of tannery wastewater. It also explains effectiveness of CEPT in removing pollutants from tannery wastewater using various metal salts. The results of this study demonstrated that the tannery effluent had high concentrations of organic matter, solids, sulfates, sulfides and chromium. Alum, ferric chloride and ferric sulfate were tested as coagulants using jar test apparatus. Alum was found to be the suitable coagulant for tannery wastewater in a dose range of 200–240 mg/L as Al 2(SO 4) 3. With alum, percentage removal efficiency for turbidity, total suspended solids (TSS), chemical oxygen demand (COD) and chromium was found to be 98.7–99.8, 94.3–97.1, 53.3–60.9, and 98.9–99.7%, respectively. National effluent quality standards for total suspended solids and chromium were met after CEPT. However, COD content was high, emphasizing the need of secondary treatment for the tannery effluent.

Enhanced Removal of Heavy Metals in Primary Treatment Using Coagulation and Flocculation

The goal of this study was to determine the removal efficiencies of chromium, copper, lead, nickel, and zinc from raw wastewater by chemically enhanced primary treatment (CEPT) and to attain a total suspended solids removal goal of 80%. Operating parameters and chemical doses were optimized by bench-scale tests. Locally obtained raw wastewater samples were spiked with heavy metal solutions to obtain representative concentrations of metals in wastewater. Jar tests were conducted to compare the metals removal efficiencies of the chemical treatment options using ferric chloride, alum, and anionic polymer. The results obtained were compared with those from other studies. It was concluded that CEPT using ferric chloride and anionic polymer is more effective than CEPT using alum for metals removal. The CEPT dosing of 40 mg/L ferric chloride and 0.5 mg/L polymer enhanced heavy metals removal efficiencies by over 200% for chromium, copper, zinc, and nickel and 475% for lead, compared with traditional primary treatment. Efficient metals capture during CEPT can result in increased allowable headworks loadings or lower metal levels in the outfall.

Recycle of Alum recovered from water treatment sludge in chemically enhanced primary treatment

An investigation was made to study the feasibility of recovering the Alum from coagulation sludges and reusing it in chemically enhanced primary treatment (CEPT) process to make the CEPT more cost-effective and recover the resource (Alum) efficiently. The optimum condition and efficiency of the acidification method for Alum recovery from coagulation sludge were investigated in the test. The results show that when the recovery rate of Alum reaches its highest level, 84.5%, the reduction rate of sludge is 35.5%. It turns out that the capability of recovered coagulant to remove turbidity, UV 254 and COD are 96%, 46% and 53%, respectively. The results prove that the recovered coagulants could be used in CEPT and the efficiency of recovered coagulant to remove pollutants is similar to that of fresh coagulant. Although some substances will be enriched during recycle, they have little effect on the quality of treated wastewater. The experiments verify that it would be an advisable and cost-effective way to recover Alum from coagulation sludges in water treatment and chemical wastewater treatment, and it could be then recycled to CEPT as well as reduce sludge volume.

Influence of Source Characteristics, Chemicals, and Flocculation on Chemically Enhanced Primary Treatment

The overall objective of this research was to investigate various methods and parameters to increase the efficiency of chemically enhanced primary treatment (CEPT). The performance of CEPT was evaluated based on its efficiency of removal of nonsettleable solids (NSS). Some of the source characteristics that influenced NSS concentration included influent total suspended solids, influent turbidity, and influent total chemical oxygen demand. A higher concentration of the influent constituents led to a higher NSS concentration, suggesting that NSS represented a somewhat fixed fraction or percent of these influent constituents. The specific particle surface area (SPSA) was found to correlate with percent NSS in the effluent. A higher SPSA is a result of smaller-sized nonsettleable colloidal particles, thus leading to an increase in percent NSS. In summary, there are several parameters that affect NSS, which could be used to control NSS to improve CEPT, as demonstrated by this study.

Synthetic polycyclic musks in Hong Kong sewage sludge

Synthetic polycyclic musks [Cashmeran (DPMI), Celestolide (ADBI), Phantolide (AHMI), Traseolide (ATII), Tonalide (AHTN), and Galaxolide (HHCB)] were determined in dewatered sludge samples from 10 major sewage treatment plants in Hong Kong using primary treatment (PT), secondary treatment (SecT) or chemical-enhanced primary treatment (CEPT) methods. The concentrations of HHCB, AHTN, AHMI and ADBI ranged from below detection limits to 78.6mg/kg dry weight. HHCB and AHTN were the two predominant polycyclic musks in sludge samples, suggesting the extensive use of these two polycyclic musks in Hong Kong. Polycyclic musk levels in CEPT sludge were significantly higher than those in SecT and PT sludge, suggesting that CEPT sludge has a higher ability to retain polycyclic musks. Comparisons to global concentrations revealed that HHCB and AHTN concentrations detected in Hong Kong sludge ranked first and second respectively. However, the estimated levels of HHCB and AHTN in the discharged effluent from sewage treatment plants may pose low potential risks to aquatic organisms according to the threshold effect levels derived for fish. Nevertheless, the polycyclic musks released in sewage treatment plant effluents may bioconcentrate and bioaccumulate in the marine environment in Hong Kong. Therefore, monitoring studies in marine ecosystems, particularly on the two prevailing polycyclic musks, are necessary.

Temporal and spatial variations in nutrient stoichiometry and regulation of phytoplankton biomass in Hong Kong waters: Influence of the Pearl River outflow and sewage inputs

In 2001, the Hong Kong government implemented the Harbor Area Treatment Scheme (HATS) under which 70% of the sewage that had been formerly discharged into Victoria Harbor is now collected and sent to Stonecutters Island Sewage Works where it receives chemically enhanced primary treatment (CEPT), and is then discharged into waters west of the Harbor. The relocation of the sewage discharge will possibly change the nutrient dynamics and phytoplankton biomass in this area. Therefore, there is a need to examine the factors that regulate phytoplankton growth in Hong Kong waters in order to understand future impacts. Based on a historic nutrient data set (1986–2001), a comparison of ambient nutrient ratios with the Redfield ratio (N:P:Si = 16:1:16) showed clear spatial variations in the factors that regulate phytoplankton biomass along a west (estuary) to east (coastal/oceanic) transect through Hong Kong waters. Algal biomass was constrained by a combination of low light conditions, a rapid change in salinity, and strong turbulent mixing in western waters throughout the year. Potential stoichiometric Si limitation (up to 94% of the cases in winter) occurred in Victoria Harbor due to the contribution of sewage effluent with high N and P enrichment all year, except for summer when the frequency of stoichiometric Si limitation (48%) was the same as P, owing to the influence of the high Si in the Pearl River discharge. In the eastern waters, potential N limitation and N and P co-limitation occurred in autumn and winter respectively, because of the dominance of coastal/oceanic water with low nutrients and low N:P ratios. In contrast, potential Si limitation occurred in spring and a switch to potential N, P and Si limitation occurred in eastern waters in summer. In southern waters, there was a shift from P limitation (80%) in summer due to the influence of the N-rich Pearl River discharge, to N limitation (68%) in autumn, and to N and P co-limitation in winter due to the dominance of N-poor oceanic water from the oligotrophic South China Sea. Our results show clear temporal and spatial variations in the nutrient stoichiometry which indicates potential regulation of phytoplankton biomass in HK waters due to the combination of the seasonal exchange of the Pearl River discharge and oceanic water, sewage effluent inputs, and strong hydrodynamic mixing from SW monsoon winds in summer and the NE monsoon winds in winter.

Particle size distribution and removal by a chemical-biological flocculation process

The particle characterization from the influent and effluent of a chemical-biological flocculation (CBF) process was studied with a laser diffraction device. Water samples from a chemically enhanced primary treatment (CEPT) process and a primary sediment tank process were also analyzed for comparison. The results showed that CBF process was not only effective for both the big size particles and small size particles removal, but also the best particle removal process in the three processes of CBF process, CEPT process, and PST process (primary sediment tanks). The results also indicated that CBF process was superior to CEPT process in the heavy metals removal. The high and non-selective removal for heavy metals might be closely related to its strong ability to eliminate small particles. Samples from different locations in CBF reactors showed that small particles were easier to aggregate into big ones and those disrupted flocs could properly flocculate again along CBF reactor because of the biological flocculation.

Different pollutants removal efficiencies and pollutants distribution with particle size of wastewater treated by CEPT process

The removal efficiency of different pollutants of wastewater treated by Chemically Enhanced Primary Treatment (CEPT) process and pollutants distribution with particle size were studied in this paper. The distributions of contaminants with particle size were studied using synthetic cellulose esters micro-porous filtering membrane of different porous size to separate the wastewater and samples after coagulation in sequence. Turbidity, UV254, COD, total phosphorus and ammonia nitrogen of the samples were measured. The results showed that the removal efficiency of the pollutants and their distributions with particle size were closely related. For contaminants in wastewater associated with particles larger than 1.2µm, the removal efficiency was very high; on the contrary, it was difficult for CEPT to remove particles smaller than 0.2µm. The removal capabilities of CEPT also correlate to the pollutants characteristics. Therefore CEPT had effective removal efficiency for total phosphorus and pollutants associated with particles larger than 1.2µm.

Comparative Study of Operation Performance and Microbial Community between Chem-bioflocculation(CBF) Process and Chemically Enhanced Primary Treatment (CEPT) Process

Chem-bioflocculation (CBF) process was a new municipal wastewater treatment process developed in recent years. The flocculant dosage was one of the most important factors in operation optimization of chem-bioflocculation(CBF) treatment process. Five levels of flocculant dosage (PAFC) from 30mg/L to 100mg/L were applied to compare operational performance between CBF process and chemically enhanced primary treatment (CEPT) process. Superior column loadings of COD, SCOD, SS, and NH4+-N were obtained in CBF process. The column loading of TP was present as close level in two processes. The biodiversities of microbial communities, including Bacteria, Acitnomycetes, Acidobacterium, and ammonia oxidizing bacteria (AOB), were analyzed by using PCR-DGGE method with group-specific primers at different flocculant dosage of polyaluminium ferric chloride (PAFC). The results indicated that CBF reactor contained special bacterial community structure other than CEPT reactor. The special distribution of bacterial population was even at different positions of two reactors. To quantify Bacteria cells, Real-Time PCR method was applied by using primers for 16SrDNA V3 regions. CBF reactor had a little less population size of Bacteria than traditional AS process, but great higher than that of CEPT reactor.

Laboratory Clarifier Test to Predict and Optimize Full Scale Chemically Enhanced Primary Treatment (CEPT) Process

Laboratory Clarifier Test to Predict and Optimize Full Scale Chemically Enhanced Primary Treatment (CEPT) Process

Adsorbent obtained from CEPT sludge in wastewater chemically enhanced treatment

Chemically enhanced primary treatment (CEPT) in municipal wastewater treatment is particularly suitable for rapidly growing cities. The focus on CEPT process now might be the cost of chemicals and disposal of chemical sludge. In this study, the potential application of adsorbent made from CEPT sludge in CEPT wastewater treatment was investigated in various conditions, such as the adsorbent dosage, pH, and dosing modes of ferric chloride and adsorbent. It was found that sludge-derived adsorbent was a good way of sludge disposal while enhanced pollutants removal rate and reduced the fresh ferric chloride dosage. With the use of 10.0 mg L −1 of ferric chloride and 0.6 g L −1 of the adsorbent at the first stage simultaneously, the enhanced removal efficiencies of turbidity, UV 254, COD, TP were 83.3%, 52.3%, 48.8% and 89.0%, respectively. The experiments showed that ferric chloride dose was reduced about 50%. The pH played a significant role in coagulation and adsorption process.

Simulation and optimization of chemically enhanced primary/activated sludge treatment for small communities

Over the last two decades, the use of coagulation and flocculation has been emphasized for the enhancement of primary sedimentation in municipal wastewater treatment plants. This work is concerned with the development of an approach for the simulation and optimization of a chemically enhanced primary treatment (CEPT)/activated sludge scheme for municipal wastewater treatment using ferric chloride as a coagulant. A mathematical model has been developed which comprises empirical relations for the CEPT stage based on reported experimental data. The activated sludge model has been based on reported rules of thumb. Optimization has been undertaken using the BOX Complex Routine to minimize a cost objective function with controlling parameters. The effect of varying operating cost components on the cost function has been also assessed via sensitivity analysis. Results indicate that, for small communities, the addition of a CEPT stage is recommended based on technical and economic consideration for current and prospective costs and prices.

Removal of Ammonium Nitrogen from Pretreated Domestic Sewage Using a Natural Ion Exchanger

Ammonium nitrogen was removed from pretreated domestic sewage using a natural zeolite-clinoptilolite, applying a column with downflow regime. The pretreated wastewater had an average total ammonium nitrogen (TAN) of 23 mg l-1. Ion exchange was allowed to take place under normal sewage treatment plant conditions and tropical temperature setting. The sorption capacity of the natural clinoptilolite was studied with the column fitted to a chemically enhanced primary treatment (CEPT)-upflow anaerobic sludge blanket (UASB) system, operating at 33°C. Optimal operational cation exchange capacity (CEC) of 14 g TAN kg-1 zeolite was obtained for the zeolite granulometry of 1-2.5 mm in a reversible way. The treatment was done at 3.9 bed volumes (BV) per day, and breakthrough was attained after about 560 BV. Regeneration of exhausted zeolite was effected with a 25 g NaCl l-1 salt solution, rendering the column amenable to reuse. Employing a 3-column test and bed contact times of 6, 2.6 and 1.1 minutes, the use of pretreated wastewater with average concentration of 38 mg NH4 +-N l-1 showed that the operational cation exchange capacity also depended on flow rate, with the removal efficiency decreasing from 95 to 47 % with increase in the flow rate. Overall, the approach of removing TAN from digested sewage offers potential to recover the TAN from the domestic wastewater, thus minimizing the need for subsequent nitrification-denitrification of the whole water volume.

Cost-effective solutions for sewage treatment in developing countries - the case of Brazil

Cost-effective solutions are a must in developing countries, not only regarding investment costs, but also in respect to technology and operating practices. With these two goals in mind, in Brazil a particular effort has been directed for the development and application of the Chemical Enhanced Primary Treatment (CEPT) process and of the Upflow Anaerobic Sludge Blanket (UASB) process, both followed by complementary secondary treatment. Both technologies are under current expansion in Brazil. Large CEPT plants have been designed and built, up to 3.7 m3/s average design flow, as well as large UASB reactors, up to 3.0 m3/s average design flow. The applied technologies are cost-effective: they present low investment and efficiencies of BOD removal of up to 50% to 70%. They allow the plant construction in steps, an initial phase with efficiency over the usual primary treatment, and in order to achieve best effluent quality and meet legal water quality standards, a logic upgrade post-treatment can later on be implemented. The higher initial reduction of BOD and TSS also permits savings in construction and operational costs of secondary treatment, due to lower organic load and lower energy consumption. Sludge represents a particular point of attention: in the cases when the CEPT was used, Chemical Stabilisation of the Sludge (CSS) has also been practiced, eliminating the high construction costs of the digesters, all the plant staying chemically operated. In the cases when the UASB is used preceding secondary treatment, sludge can easily return to the anaerobic vessel, the costly sludge digestion unit being avoided. UASB reactors have practically no equipment in the anaerobic vessel, no energy consumption, low sludge production, and when applied in hot climates as in Brazil, heating devices are not required. The Brazilian experience, some particular cases, special comments on design and different secondary treatment processes are presented in this paper, as a contribution to the discussion of cost and benefits, a prime point to be considered.

Removal of carbon and nutrients from domestic wastewater using a low investment, integrated treatment concept

An integrated chemical–physical–biological treatment concept for the low-cost treatment of domestic wastewater is proposed. Domestic wastewater was subjected to a chemically enhanced primary treatment (CEPT), followed by treatment in an upflow anaerobic sludge blanket (UASB) reactor. In addition, a regenerable zeolite was used to remove NH 4 +, either after CEPT pretreatment or after biological treatment in the UASB reactor. The CEPT pretreatment consisted of the addition of a coagulant (FeCl 3) and an anionic organic flocculant and removed on average 73% of the total chemical oxygen demand (COD t), 85% of the total suspended solids, and 80% of PO 4 3− present in the wastewater. The UASB system, which consequently received a low COD t input of approximately 140 mg/L, was operated using a volumetric loading rate of 0.4 g COD t/L. d (hydraulic retention time [HRT]=10 h) and 0.7 g COD t/L. d (HRT=5 h). For these conditions, the system removed about 55% of the COD t in its influent, thus producing an effluent with a low COD t of approximately 50 mg/L. The zeolite, when applied in batch mode before the UASB reactor, removed approximately 45% of the NH 4 +, whereas its application as a post-treatment cartridge resulted in almost 100% NH 4 + removal. The simple design and relatively low operating costs, due to low costs of added chemicals and low energy input (estimated at € 0.07–0.1 per m 3 wastewater treated), combined with excellent treatment performance, means that this system can be used as a novel domestic wastewater treatment system for developing countries. Therefore, the system is called a Low Investment Sewage Treatment (LIST) system.

Geotechnical characterization of dewatered sewage sludge for landfill disposal

The disposal of increased quantities of dewatered sewage sludge to landfills may cause geoenvironmental problems such as leachability, total and differential settlement, and slope stability of the waste during disposal. This study investigates the geotechnical properties of the dewatered sewage sludge generated from chemically enhanced primary treatment (CEPT) in Hong Kong. Compaction test results show that CEPT sludge exhibits compaction characteristics similar to those of clayey soils; however, the lowest hydraulic conductivity of CEPT sludge does not occur near the wet side of its optimum water content. The consolidation behavior of CEPT sludge does not follow the conventional Terzaghi's theory. Under an overburden pressure higher than 24 kPa, the relationship between the logarithm of the hydraulic conductivity (logk) and the void ratio (e) is linear. Results from direct shear tests reveal that, for CEPT sludge, slopes of 20° can probably be constructed during the landfill operation without causing sliding problems. Compared with the disposal of pure CEPT sludge, the co-disposal of dewatered sewage sludge with other solid wastes commonly found in Hong Kong results in lower compressibility, smaller settlement, but higher hydraulic conductivity.Key words: co-disposal, geotechnical properties, landfill disposal, sewage sludge.