Primary Sedimentation Process Research Articles

Health Risk Assessment for Reused Backwash Water from Saveh Water Treatment Plant

Background: The increase in population growth, industries and living standards have caused an increasing need for drinking water in many countries. The reuse of treated water and wastewater is one of the most important options to deal with water shortage. To ensure the correctness of this work, it is necessary that the health risk assessment be reassessed during use so that consumers do not face serious problems. In this regard, the assessment of health risks assessment for the water recovered from the backwashing wastewater of the Saveh water treatment plant was investigated. Methods: To reuse the backwash wastewater from the Saveh water treatment plant, the processes of primary sedimentation and coagulation (in the form of a test jar) were investigated. Metals and heavy metals like iron (Fe), aluminum (Al), lead (Pb), Arsenic (As) and cadmium (Cd) were examined to evaluate health risks. The initial settling time was 1 hour, the coagulant used was FeCl3 made in Iran, and heavy metal contents were also measured with an Inductively coupled plasma (ICP) device. Results: The value of HRIs for Al, Fe, As, Pb and Cd in the treated spent filter backwash water (SFBW) with primary sedimentation and coagulation was less than "1" and indicates the absence of risk. Conclusion: The treated backwash wastewater treated with primary sedimentation and coagulation processes as well as raw water of the Saveh have no harmful effects in terms of heavy metals, and its reuse will not pose a risk to the health of the consumer.

A long aging time had severely inhibited methane production from Fe-chemically enhanced primary sedimentation sludge during anaerobic digestion

Fe-chemically enhanced primary sedimentation (CEPS) process is a cost-effective method to capture organics from municipal wastewater into Fe-CEPS sludge. Anaerobic digestion (AD) has been proven to be an efficient and economical method to treat Fe-CEPS sludge. Meanwhile, the CEPS sludge produced by sedimentation is generally stored on-site for days to months. During this period, different iron species in Fe-CEPS sludge can form, potentially influencing subsequent methane production. Thus, this study investigated the biodegradability of Fe-CEPS sludges after different aging times, ranging from 0 to 35 days, during the AD process. The results indicated that iron-bearing species gradually transformed into more crystalline phases, with the content increasing from 6.17 to 21.72 mg/g as the aging time extended. Furthermore, the highest methane yield was obtained from the fresh Fe-CEPS sludge, reaching a value of 186.18 mL CH4/g TS. However, with increasing aging time, methane yields significantly decreased, reaching the lowest yield of 35.73 mL CH4/g TS in the group with an aging time of 35 days. This suggests that prolonged aging time severely inhibits methane production from Fe-CEPS sludge. Significant negative relationships were observed between methane yield and vivianite-P, crystalline iron (Cry-Fe) (r = −0.97, p < 0.01; r = −0.94, p < 0.01). Conversely, the TOC content of the aged sludges exhibited a strongly positive correlation with methane yield (r = 0.88, p < 0.05). These findings suggest that the formation of vivianite-P, Cry-Fe, and microbiological oxidation resulting from prolonged aging times are the main contributors to inhibiting subsequent methane production.

Comparison of the elimination effectiveness of tetracycline and AmpC β-lactamase resistance genes in a municipal wastewater treatment plant using four parallel processes.

Municipal wastewater treatment plants (mWWTPs), considered reservoirs of antibiotic resistance genes (ARGs), are selected to compare the contributions of technology and process to ARG removal. Fifteen ARGs (tetA, tetB, tetC, tetE, tetG, tetL, tetM, tetO, tetQ, tetS, tetX, MOX, CIT, EBC, and FOX) and two integron genes (intI1, intI2) were tracked and detected in wastewater samples from a large-scale mWWTP with four parallel processes, including three biological technologies of AAO (anaerobic-anoxic-oxic), AB (adsorption-biodegradation), and UNITANK, two different disinfection technologies, and two primary sedimentation steps. The results showed that ARGs were widely detected, among which tetA and tetM had the highest detection rate at 100%. AAO was the most effective process in removing ARGs, followed by the AB and UNITANK processes, where the separation step was critical: 37.5% AmpC β-lactamase genes were reduced by the secondary clarifier. UV disinfection was more efficient than chlorination disinfection by 47.0% in ARG removal. Both disinfection and primary sedimentation processes could effectively remove integrons, and the swirling flow grit chamber was a more effective primary settling facility in total ARG removal than the aerated grit chamber. The tet genes and AmpC β-lactamase genes were significantly correlated with the water quality indexes of BOD5, CODCr, SS, TP, TOC, pH and NH4+-N (p < 0.05). In addition, the correlation between efflux pump genes and AmpC β-lactamase genes was strongly significant (r2 = 0.717, p < 0.01). This study provides a more powerful guide for selecting and designing treatment processes in mWWTPs with additional consideration of ARG removal.

Impact of differences in speciation of organic compounds in wastewater from large WWTPs on technological parameters, economic efficiency and modelling of chemically assisted primary sedimentation process

The aim of the study was to supplement the information missing in the literature on the influence of organic compounds speciation (percentage of chemical oxygen demand (COD) fractions, readily biodegradable and non–biodegradable dissolved organic matter; slowly biodegradable and non‒biodegradable insoluble organic matter) in wastewater on chemically assisted primary sedimentation process and its potential impact on the energy and economic balance of the plant. The statistical modelling of the chemically assisted primary sedimentation process using artificial neural networks (ANN) was a novelty. It was also important to check the differences resulting from the use of coagulants, polyelectolites and their doses. For both large wastewater treatment plants (>500,000 people equivalent) located in the various regions of the country in Central Europe only ferric chloride had a positive balance. The addition of polyelectrolyte in the Wroclaw wastewater did not affect the chemically assisted primary sedimentation process but in the Bialystok wastewater it strengthened the process effect. In both plants only doses from 10 to 40 mgFe/dm3 are cost-effective. The results indicate that the addition of polyelectrolyte should be taken into account in this application and was correlated with the amount of colloidal COD fractions in wastewater. The developed ANN models reflected well the effectiveness of COD removal in both large WWTP while the sensitivity analysis of individual ANN models showed differences in the variables affecting the calculation process of both models, despite similar values of parameters characterizing wastewater in both wastewater treatment plants.

Wastewater Treatment Plant and Wetland Design Analysis (Case Study in Samosir, North Sumatera)

Lake Toba, North Sumatera is one of the national tourism areas in Indonesia that has water pollution problem due to the unsustainable development especially in the catchment area. To support Lake Toba Tourism Area and to educate the people about sustainable development, Ministry of Public Works and Housing, Republic of Indonesia built integrated tourist toilets equipped with wastewater treatment plant at Menara Pandang Tele Area, one of the most strategic tourism attraction located in the catchment area of Lake Toba. The wastewater treatment plan is not only to use biofilter but also Kolam Sanita (wetland) as secondary treatment. This study would like to see how the wastewater treatment plant at Menara Pandang Tele is designed and see what modification are made from the original design to make it well functioned. This study uses a quantitative method to calculate the volume of the wastewater treatment plant. Further calculation is also needed to determine the dimension of the technologies. The geographical character is the main aspect to be considered in this step. The results showed that to meet the quality standard of the wastewater, the biofilter technology is determined to use three processing stages starting with equalization, primary sedimentation, and secondary process which consist of anaerobic process and clarifier. The dimension modification must not be more than two meters in height. Kolam Sanita is needed to make sure the effluent quality will not harm the groundwater. The modification is required due to the various heights of the ground level and makes the design representative of aesthetic function.

Combined chemically enhanced primary sedimentation and biofiltration process for low cost municipal wastewater treatment

The main objective of wastewater treatment is to remove carbon and other nutrients from municipal and industrial effluents in order to protect the environment and human health. Typical wastewater treatment is usually achieved by a combination of physical, chemical and biological methods. In this work, municipal wastewater was depurated using chemically enhanced primary treatment (CEPT) in combination with a pilot-scale trickling filter. Lab scale experiments (Jar-tests) were carried out in order to determine the optimum dosage of chemicals. Selection criteria were the organic load removal efficiency and the low operational cost. Coagulation-flocculation process was conducted through polyaluminium chloride (PAC) and the cationic polyelectrolyte (Zetag 8180) addition. By combining CEPT and trickling filter, tCOD (total Chemical Oxygen Demand), sCOD (soluble Chemical Oxygen Demand), BOD5 (5-day Biochemical Oxygen Demand), NH4+-N, TSS (Total Suspended Solids), VSS (Volatile Suspended Solids) and PO43−-P removal efficiencies were estimated to be 89, 82, 93, 60, 96, 96 and 78%, respectively. It is concluded that biological filtration contributed significantly in nutrients removal processes. Moreover, the obtained effluent was low in carbon and rich in nitrogen, which can be applied for restricted irrigation after disinfection, complying with the discharge limits set in the Greek Joint Ministerial Decree 145116/2011.

Seasonal occurrence and fate of chiral pharmaceuticals in different sewage treatment systems in Hong Kong: Mass balance, enantiomeric profiling, and risk assessment

Concern about the presence of chiral pharmaceuticals in the environment from wastewater discharge is mounting. In this work, the occurrence and fate of atenolol, metoprolol, venlafaxine, and chloramphenicol, including 10 different stereoisomers, were investigated in sewage and sludge from diverse treatment processes in 4 sewage treatment plants (STPs) in Hong Kong via 4 sampling campaigns over a period of 2 years. The average amounts of individual pharmaceuticals entering the STPs ranged from 4.91 g/d to 6290 g/d, with sludge carrying much lower amounts than the discharged effluent. Mass balance analysis revealed that: larger quantities of these pharmaceuticals were released during the dry seasons, biodegradation was the primary removal mechanism for atenolol and chloramphenicol, and the removal via primary sedimentation and disinfection processes was insignificant (<30%). Selectivity toward R-(+)-atenolol, S-(−)-metoprolol, and R-(−)-venlafaxine was mostly found across secondary-treated effluent samples. Sold as an enantiopure pharmaceutical in R,R-para-form, chloramphenicol was preferentially eliminated after biological process. This is the first study on the occurrence of chloramphenicol enantiomers in the aquatic environment. Ecotoxicological assessment indicated that atenolol and metoprolol could pose risks to marine fish in effluent-receiving waters (i.e., the western waters and Victoria Harbor) of Hong Kong, while R-(+)-atenolol could pose a risk to protozoans five times higher than the S-(−)-enantiomer.

Model of Suspended Solids Removal in the Primary Sedimentation Tanks for the Treatment of Urban Wastewater

Primary settling tanks are used to remove solids at wastewater treatment plants and are considered a fundamental part in their joint operation with the biological and sludge treatment processes. The aim of this study was to obtain a greater understanding of the influence of operational parameters, such as surface overflow rate, hydraulic retention time, and temperature, on the removal efficiency of suspended solids and organic matter by the measurement of chemical oxygen demand and biochemical oxygen demand in the primary sedimentation process. The research was carried out in a semi-technical primary settling tank which was fed with real wastewater from a wastewater treatment plant. The physical process was strictly controlled and without the intervention of chemical additives. Three cycles of operation were tested in relation to the surface overflow rate, in order to check their influence on the different final concentrations. The results obtained show that the elimination efficiency can be increased by 11% for SS and 9% for chemical oxygen demand and biochemical oxygen demand, for variations in the surface overflow rate of around ±0.6 m3/m2·h and variations in hydraulic retention time of around ±2 h. The results also show that current design criteria are quite conservative. An empirical mathematical model was developed in this paper relating SS removal efficiency to q, influent SS concentration, and sewage temperature.

Recovery of organic carbon and phosphorus from wastewater by Fe-enhanced primary sedimentation and sludge fermentation

Abstract A new chemically enhanced primary sedimentation (CEPS) and sludge fermentation process are developed for improved nutrient removal, energy saving and resource recovery in municipal wastewater treatment. The FeCl3-based CEPS with a dosage of 20 mg-Fe/L can remove 75.6% of organic pollutants and 99.3% of PO4-P on average from wastewater. Under natural fermentation conditions, the CEPS sludge undergoes effective hydrolysis and acidogenesis to produce volatile fatty acids (VFAs) and release phosphate as valuable resources. By using CEPS, around 27% of the organic carbon in wastewater influent can be recovered via sludge fermentation, mainly in the form of VFAs, and about 23% of phosphorus recovered for making vivianite fertilizer. In comparison, both the organic and phosphorus recovery ratios from wastewater are under 10% with conventional primary sedimentation and sludge fermentation. CEPS combined with side-stream sludge fermentation can be readily applied in new treatment plants or in a retrofit of existing treatment systems.

Co‐development of alluvial fan surfaces and arid botanical communities, Stonewall Flat, Nevada, USA

ABSTRACTArid alluvial fan and fluvial dry wash surfaces in Stonewall Flat, Nevada, USA, are characterized using surface geomorphic surveys, soil pits, botanical line surveys, and varnish microlamination dating techniques. Active and abandoned washes, and active fan surfaces are dominated by primary geomorphic processes of high‐energy sedimentation from flash floods. These surfaces are characterized by bar and swale topography, a lack of stone pavements, soil horizons, and rock varnish. Younger terraces and slightly older intermediate fan surfaces are in transition from primary sedimentation processes to lower energy secondary surface‐modifying processes of sheet wash and eolian transport and deposition. These surfaces are characterized by faint to no bar and swale topography, incipient to moderately well‐developed pavements and soil horizons, and abundant coppices. Old and stable fan surfaces are dominated by lower energy secondary processes and manifest well‐developed pavements, soils, and sparse coppices around widely distributed shrubs. Varnish microlamination dating yields ages of 13·15 ka for intermediate fan surfaces and 25·55 to 86·75 ka for stable fan surfaces. Plant communities co‐developing with these surfaces affect and are affected by both primary and secondary geomorphic fan processes. Relatively active surfaces contain few woody species. Co‐dominance of shrubs and annuals with abundant annuals between the shrubs is characteristic of surfaces transitional from primary processes to secondary processes. Stable surfaces dominated by secondary processes are characterized by woody perennials, with long‐lived woody species inhabiting the oldest surfaces. Feedback mechanisms between early botanical communities and eolian deposition affect coppice and pavement development. In turn, these surface features control both the composition and distribution of botanical communities on older, more stable surfaces. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Efficient treatment of real textile wastewater: Performance of activated sludge and biofilter systems with a high-rate filter as a pre-treatment process

This study was conducted to evaluate the performance of High-Rate Filter (HRF) as an alternative process to Conventional Primary Sedimentation (CPS) processes and the performance of different configurations of activated sludge and biofilter systems with anaerobic/aerobic zones for efficient textile wastewater treatment. The performance efficiency of the HRF with much shorter hydraulic retention time (HRT: 0.3 h) was very similar to that of the CPS process with a longer HRT of 3.0 h. The highest efficiencies of the systems were achieved by configuring anoxic:anaerobic:oxic:oxic zones for an activated sludge system and anaerobic:oxic: anoxic zones for a biofilter system, respectively. In particular, under the most efficient configurations of the systems, the performance of the biofilter system achieved a higher efficiency than that of the activated sludge system. Compared with the existing physicochemical-sequencing batch reactor system, the most efficient configurations of the HRF/activated sludge system and the HRF/biofilter system with a shorter HRT achieved both higher pollutant removal efficiency and lower sludge production.

ED-WAVE tool design approach: case of Limbe wastewater treatment works, Blantyre, Malawi

The ED-WAVE tool is a PC based package for imparting training on wastewater treatment technologies. The system consists of four modules viz. Reference Library, Process Builder, Case Study Manager, and Treatment Adviser. The principles of case-based design (CBD) and case-based reasoning (CBR) as applied in the ED-WAVE tool are utilised in this paper to evaluate the design approach of Limbe wastewater treatment works (Limbe WWTW) in Malawi. The plant has an average dry weather flow rate of 1,800 m3/d. The study established that a similar case to both the dry season and wet season conditions of Soche wastewater treatment works has similarities to Municipal Case 1 in Sri Lanka, with a flow rate of 1,700 m3/d. The study further established that that there are certain unit treatment processes that are important in wastewater treatment. These include a primary sedimentation process, achieved through the imhoff tank at the plant in Sri Lanka, chemical precipitation followed by sedimentation as suggested by the dr...

Short-term hydrographic variability in a stratified Arctic fjord

AbstractFjords in the Arctic often have a more complex circulation pattern than the classical two-dimensional estuarine circulation. This is due to the effects of the Earth's rotation on stratified waters in wide fjords. Observations from a semi-enclosed fjord basin, Van Mijenfjorden on Spitsbergen, show that the hydrography and circulation vary considerably on short timescales (hours) in the summer season. The depth and distribution of the low salinity upper water layer respond quickly to changes in the wind field. The Coriolis effect has an essential impact on the circulation, inducing eddy-like flow patterns and strong cross-fjord gradients. Within the upper layer, the lowest salinity values and highest temperatures were found on the northern side of the fjord in calm wind periods. When the wind was strong from the west, the cross-fjord gradients were reversed. Internal wave activity contributes to large vertical displacement of water below the upper layer. Knowledge of such strongly variable hydrographic conditions in fjords are important for sampling strategy and interpretation of data, for instance of primary production and sedimentation processes, and for the understanding of fjords as depositional systems.

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.

A combined transfer-function noise model to predict the dynamic behavior of a full-scale primary sedimentation tank

Studying how and to what extent effluent TSS and COD are related to influent TSS, COD, and flow in a primary sedimentation process is the objective of this paper. The analysis is based on data collected hourly over two periods of sampling, each lasted 1 week at an Edmonton, Alberta sewage treatment plant. In order to establish a dynamic model for the system, the methodology of Box and Jenkins (Time series Analysis: Forecasting and Control, Holden-Day, Oakland, CA, 1976) was utilized. With this approach, stochastic and transfer-function components can be combined to form a dynamic model and the relative importance of these two components can be quantitatively assessed. The models were able to explain the data very well. Using the models as parts of a real-time control scheme was also discussed.

The Impact of Residual Coagulant on the Respiration Rate and Sludge Characteristics of an Activated Microbial Biomass

Pre-precipitation is widely used in wastewater treatment to increase the removal of suspended solids (SS) and chemical oxygen demand (COD) in the primary sedimentation process. During pre-precipitation, a portion of the coagulant is removed from the treatment system in the primary settled sludge. However a residual amount will remain in the supernatant which is then treated by the secondary, biological treatment process. The effect of direct coagulant addition to the secondary biological treatment stage, known as simultaneous precipitation, is well documented but the effect of residual coagulant on secondary biological treatment as a result of pre-precipitation has received little attention. Jar tests were optimized with respect to SS, COD and phosphorus (P) removal at influent pH—between pH 7–8. Optimum dose was found to be 25 mgl −1 as metal ion for both alum and ferric sulphate coagulants. The residual metal concentration in the primary settled wastewater from the jar test experiments was identified as being 1.94 and 1.98 mg Fel −1 for ferric sulphate coagulants and 0.90 mg All −1 1 for alum. Primary effluent was fed to a settled activated microbial biomass to give total solids concentration of 2.0–2.5 g1 −1 . The impact of residual metal concentration on (i) respiration rate and COD removal and (ii) species diversity and floc structure were investigated. This paper presents the results of a laboratory-scale screening experiment undertaken to consider the impact of residual iron and aluminium coagulants on the secondary treatment process. Results identify a link between low level concentrations of coagulant, and reduction in microbial activity, changes in species diversity and floc morphology highlighting the importance of a bench/pilot-scale study.

Microbial processes in the formation of the Sinian Gaoyan manganese carbonate ore, Sichuan Province, China

Based on a detailed study of ore fabrics, microbial remains, stable isotopes, and organic matter, the characteristics of the Late Sinian Gaoyan Mn-carbonate ores can be summarized as follows: (1) Ores have massive, laminated, spheroid-banded, and spheroidal structures. (2) Microbial remains, such as Sphareocongregus variabilis (Moorman, 1974) and Eoentophysalis sp. occur in the ores. (3) The ores contain abundant rhodochrosite, pyrite, and siliceous microframboids and possibly also multicellular magnetotactic aggregates. (4) Ca rhodochrosite in spheroidal ores always has a fibrous texture, similar to that of calcite reported to form as a product of bacterial fermentation. (5) The organic matter of ore samples records a relatively mild thermal history (up to catagenesis). Hopane and sterane indicate that bacteria and algae were the likely sources of the organic matter. (6) The mean value of δ 13 C PDB for micritic dolostone overlying the ore beds is −3.3‰, and for Mn-carbonate ores, −4.9‰. No positive correlation exists between the MnO content and δ 13 C PDB values, which is used as an indicator of enrichment of Mn in rhodochrosite formed during sulfate reduction. The above characteristics indicate that the Gaoyan Mn-carbonate ores were rich in organic matter and that sulfate reduction during early diagenesis was well developed. However, δ 13 C PDB values of Mn-carbonate ores are not consistent with formation solely in the zone of sulfate reduction. It is also difficult to explain the carbon source of the Gaoyan carbonate ores as being only from seawater bicarbonate and CO 2 produced during sulfate reduction. We suggest that an integrated model for the origin of Gaoyan Mn-carbonate ores must include a combination of primary sedimentation, sulfate reduction, and fermentation processes.

The use of ferric chloride and anionic polymer in the chemically assisted primary sedimentation process

Chemically Enhanced Primary Treatment (CEPT) or Chemically Assisted Primary Sedimentation Process (CAPS) involves the use of chemical coagulants to enhance the coagulation or flocculation of wastewater particles. The effect of a metal salt, ferric chloride (FeCl 3) and an anionic polymer on the removal of suspended solids (SS) of wastewater collected from two sewage treatment plants was studied by jar test experiments. The results showed that the optimum dosage for the removal of 60% of SS was 30 ppm of FeCl 3 with 0.5 ppm polymer. A larger scale test further revealed that the addition of 30 ppm of FeCl 3 and 0.5 ppm. polymer could provide a reduction of SS, total nitrogen (N) and total phosphorous (P) higher than 80%, 70% and 40%, respectively. The experimental results confirmed that CAPS can be used as an alternative for the treatment of sewage to traditional biological processes.

Dewaterability of alum and ferric coagulation sludges

Ferric sulfate sludges demonstrated superior dewaterability over sludges formed by coagulation with aluminum.Tighter regulations governing stream discharge of coagulation sludge from the primary sedimentation process prompted the University of Iowa Water Treatment Plant to consider sludge‐handling options. This pilot study was undertaken in order to investigate differences in the mechanical dewatering of sludges formed by using either alum or ferric sulfate coagulants. The approach used various volumes of wasted lime sludge produced from the plant's softening process as a filtering aid. After the short pilot study, dewatering data from a bench‐scale plate‐and‐frame filter press indicated that ferric sludge was easier to dewater than sludges formed by coagulation with alum. The addition of lime‐softener sludge increased the dewaterability of all sludges tested, primarily by increasing the sludge feed solids concentration, which may have also decreased blinding.

Differential sedimentation versus coring artifacts: a comparison of two widely used piston-coring methods

In order to compare two widely used piston-coring techniques, parallel cores were taken with both a Kullenberg and a Livingstone corer in the deepest part of Soppensee (25 m), a small eutrophic Swiss lake containing varved sediments. The cores were taken within a horizontal distance of 3 m and yield comparable stratigraphic records. Differences in millimetre-scale microstructure are attributed to primary sedimentation processes at the water/sediment interface. Sediment thin-sections, as well as sediment x-radiograph investigations, reveal no difference in microstructure that could unequivocally be attributed to one of the coring methods used. The differences in deposition are therefore thought to reflect the inherent variability of lacustrine sedimentation in Soppensee. Major differences in overall core recovery do occur, however, in organic-rich, highly porous sediments. These variations are primarily attributed to differential gas expansion. Actual sediment-accumulation rates can therefore only be correctly estimated if the sedimentary record can be constrained within a high-resolution temporal framework, e.g. by annual laminations.