Stabilization Ponds Research Articles

Laboratory-scale waste stabilisation pond development

The present study describes the development of a laboratory-scale waste stabilisation pond (WSP) system, undertaken in order to investigate the effects of hydraulic, physicochemical, microbial and physical parameters on wastewater treatment. Previous studies have focused predominantly on hydraulic characteristics. This system was engineered at a scale much smaller than had previously been seen in the literature. The scale of the model used here allows for improved optimisation at a shorter time scale that would be seen for larger pilot-scale systems. Additionally, with the addition of viruses, a smaller scale model allows for more control over viral concentration used. Once constructed, the system was dosed with wastewater from a wastewater treatment plant and both the influent and effluent were monitored using common testing methods as well as direct viral analysis. Successful wastewater treatment was seen in terms of reduction of indicator bacteria and virus, as determined by culture-based methods. This treatment and the associated stabilisation of physicochemical parameters such as dissolved oxygen and pH, indicates the successful development of a microbial community within the laboratory-scale WSP.

Opuntia ficus-indica is an excellent eco-friendly biosorbent for the removal of chromium in leather industry effluents

In Brazil, the leather industry is an important economic segment moving around U$ 3 billions of dollars a year. However, high amounts of water are requested to transform skin animals into leather, causing high wastewater amounts to be consequently produced. A major problem is attached to the presence of chromium in the wastewater from the tanning process. Chromium is a heavy metal potentially toxic both to the environment and to the human health. In order to control the levels of chrome dumped into the environment, Brazilian agencies require the treatment of effluents by the generating source. Thus, this study aimed to develop an alternative method to the removal of chromium in wastewater from the leather industry using the Opuntia ficus-indica biomass as eco-friendly biosorbent. Crude waste samples were collected in a tannery stabilization pond for chromium quantification and further treatments. The powdered Opuntia ficus-indica was obtained from species collected in Pernambuco, Brazil, and its physical parameters and pHPCZ were characterized. Adsorptions studies and acute toxicity were also carried out. The biomass remaining after the sorption was analyzed through scanning electron microscopy and Fourier-transform infrared spectroscopy. The chromium content was above the limit allowed by the Brazilian regulatory agency. In sorption studies, biomass was able to remove 74.8% and 84.88% of Cr (III) using 2.0 g and 4.0 g of biomass, respectively. The surface of biomass is very favorable to biosorption and the chemical bindings among oxygen atoms present in the chemical components of this biomass and the heavy metal was confirmed through infrared spectrum. This study proved that Opuntia ficus-indica is effectively biosorbent to chromium, promising and with low costs for the leather industry, able to reduce its ecotoxicity as proven by chemical and biological assays.

Determination of Heavy Metals in Groundwater Around Al-Buraihi Sewage Station in Taiz City, Yemen.

Background.In recent years, mitigation of groundwater contamination resulting from the limited availability of freshwater for domestic use has become an important issue. The presence of heavy metals in water could have adverse effects on both plant and animal life.Objectives.The main objective of the present study was to determine possible heavy metal contamination in groundwater around Al-Buraihi sewage station in Taiz, Yemen and to understand possible sources of contamination and their relationships with groundwater.Methods.Wastewater samples were collected from a wastewater stabilization pond from Al-Buraihi sewage station and borewell water samples were collected from the vicinity. The presence of heavy metals was quantified using inductively coupled plasma-optical emission spectrometry (ICP-OES). Pearson correlation test was performed to understand the relationship between wastewater and groundwater samples.Results.Physical variables including pH, electrical conductivity (EC), dissolved oxygen (DO) and temperature and elements such as silver (Ag), arsenic (As), aluminum (Al), barium (Ba), boron (B), cadmium (Cd), chromium (Cr), iron (Fe), molybdenum, nickel (Ni), selenium (Se) and zinc (Zn) exceeded the permissible limits recommended by international standards in wastewater samples.Conclusions.Treated sewage wastewater in the study area is not suitable for irrigation as the elements/heavy metals are accumulated in soil and plants and may be accumulated in humans and animals through bio-accumulation. In addition, these heavy metals reach the water table and aquifers through percolation, thereby polluting groundwater.Competing Interests.The authors declare no competing financial interests.

Investigating the working efficiency of natural wastewater treatment systems: A step towards sustainable systems

Abstract Globally, wastewater is a vital resource and requires appropriate treatment management strategies. Wastewater has become a major source of irrigation in the peri-urban areas of developing nations. With the increasing amount of wastewater generation, there are several complications in using treatment systems in terms of installation, operation and maintenance, and size in developing countries. Recently, natural treatment systems are gaining popularity due to less cost and maintenance and have been preferred in peri-urban settings. In this study, the working efficiency of the natural systems was assessed from case studies from Vizianagaram, Andhra Pradesh, India. The nutrient (Phosphorous and Nitrogen content) and organic matter removal efficiency of four natural treatment systems (NTS) having different operation, maintenance and loading rates were investigated. The study showed that natural treatment systems have good potential for peri-urban wastewater treatment. It was also observed that waste-stabilization based systems perform better than those based on duckweed and hyacinth plants. Regularly maintained and operated systems show removal efficiency on the order of 80% for organic and nutrients and performed better than others. The study indicates that decentralized, adequately maintained Waste Stabilization Ponds (WSP) offer a viable, self-sustaining and eco-friendly alternative for wastewater treatment to supply irrigation water in rural areas.

Genome Sequences of Microviruses Identified in a Sample from a Sewage Treatment Oxidation Pond

Oxidation ponds are often used in the treatment of sewage as an aeration step prior to discharge. We identified 99 microvirus genomes from a sample from a sewage oxidation pond. This diverse group of microviruses expands our knowledge of bacteriophages associated with sewage oxidation pond ecosystems.

The application of steel slag in a multistage pond constructed wetland to purify low-phosphorus polluted river water

To investigate the effect of a constructed wetland (CW) with steel slag as the filler on water contaminated by low phosphorus levels, a multistage pond CW system was designed in this study. Low-phosphorus polluted river water was used as the research object. This study explored the effects of using steel slag as a CW filler on phosphorus removal and the total phosphorus (TP) purification effect of the wetland system. The results showed that the TP removal rates in the ecological pond, oxidation pond, surface flow wetlands and submerged plant pond were 5.17%, 8.02%, 21.56%, and 16.31%, respectively. Intermittent increases in phosphorus concentration were observed in the reactors and were caused by the decay of plant tissues, which released pollutants. Because steel slag was added to the filler, the TP concentrations in the effluent of the first- and second-level horizontal subsurface CWs increased by 151.13% and 16.29%, respectively, compared to the influent concentration. The 20th to 40th days of the test run was a period of rapid phosphorus release of the system. The use of steel slag has a potential risk of phosphorus release when applied in CWs used to purify low-phosphorus contaminated water bodies.

Transformation of Waste Stabilization Ponds: Reengineering of an Obsolete Sewage Treatment System

Waste Stabilization Ponds (WSPs) are commonly used for sewage treatment. These systems are composed of a series of ponds: (1) anaerobic ponds, (2) facultative ponds, and (3) maturation ponds. WSPs generally produce good-quality effluent in terms of organic matter and pathogen removal, but their application has disadvantages. The most serious disadvantages are a long retention time, the release of biogas, and the impossibility of removing nutrients. A promising alternative to the use of WSPs is replacing the anaerobic pond and facultative pond with an upflow anaerobic sludge blanket (UASB) reactor, with the advantages of greatly reducing the retention time and the biogas capture. The post-treatment ponds of the UASB reactor effluent involve oxygen production and the biological consumption of carbon dioxide, which raises the pH. An experimental investigation showed that it is possible to use polishing ponds in a sequential batch regime instead of continuous flow. This modification accelerates the decay of pathogens and accelerates the increase in pH, which, in turn, facilitates the removal of nitrogen and phosphorus. This produces a good-quality effluent with low concentrations of biodegradable organic material, nutrients, and pathogens. This good-quality effluent is obtained in a system without energy consumption or auxiliary materials and with a much smaller area than conventional stabilization ponds.

Diversity of algal species present in waste stabilisation ponds and different factors affecting its enrichment and phototaxis

ABSTRACT Several algal species were found in the samples collected from a wastewater treatment plant located in Uttarakhand, India. Several media and their modifications were employed to understand the role of these elements and compounds in the species composition and proliferation. Euglena, Chlamydomonas-reinhardtii, Chlorella-sorokiniana, Chlorococcum, several diatoms and cyanobacteria were found in the wastewater samples. In stagnant and flowing municipal wastewater, Euglena, Chlorococcum, cyanobacteria and Volvox were predominant. In a bold basal medium, Scenedesmus and several diatom species were observed along with Chlorococcum. In the presence of acetate Selenastrum species were abundant. Metagenomic analysis of wastewater collected during winter revealed that Tetradesmus wisconsinensis (21.23%) and Actinastrum hantzchii (11.48%) were the dominant species. Some cyanobacterial species accumulated near the high-intensity light region. Hence, subsequent phototaxis experiments were performed. Under the white light, most species showed positive phototaxis. However, under the blue and red light, all the algal species present in the sample showed negative phototaxis. Under the green light, Chlorococcum and Chlamydomonas showed positive phototaxis and Euglena showed negative phototaxis. However, under the pink light, neither negative nor positive phototaxis was observed. Hence, the obtained results provided new insights into the effects of the studied parameters on the species’ diversity and proliferation.

A new anti-fouling polysulphone nanofiltration membrane blended by amine-functionalized MCM-41 for post treating waste stabilization pond's effluent

Developing an effective and stable separation membrane for water treatment is of much interest while challenging because of the restrictions of membrane fouling and water flux reduction. To minimize this problem, in this work, highly porous and hydrophilic nanostructure of NH2-modified MCM-41 (NH2-MCM-41) was embedded successfully into the nanofiltration (NF) membrane body via commonly used phase inversion method. The unmodified and modified nanofiller was analyzed by Fourier Transform Infrared (FTIR) spectroscopy, X-Ray powder diffractometry (XRD), field emission scanning electron microscopy (FE-SEM), thermogravimetric analysis (TGA), and nitrogen adsorption–desorption. Furthermore, the modified membranes were characterized through surface and cross section FE-SEM images, the membrane surface roughness, hydrophilicity, antifouling properties and dye rejection. Benefiting from porous networks and enhanced hydrophilicity, the mixed matrix membranes (MMMs) revealed more prominent hydrophilic property as well as higher pure water flux (PWF) compared with naked membrane. The polysulphone (PSf) membrane modified with NH2-MCM-41-1.0 exhibited the highest pure water flux (PWF) of 65.43 kg/m2.h and superior antifouling characteristics with a flux recovery ratio (FRR) of around 97.0% and an irreversible fouling resistance (Rir) of 3.2%. Furthermore, the optimal membrane possessed high dye rejection (100%) and antifouling capacity (FRR of 97%) while filtering a field sample, effluent from a local stabilization pond treating municipal wastewater. The fabricated membrane in this study is believed to pave pathways for constructing NF membranes with superior effectiveness for other municipal and industrial wastewaters treatment.

Evaluation of the performance of Mzuzu Central Hospital wastewater oxidation ponds and its effect on water quality in Lunyangwa River, Northern Malawi

Mzuzu Central Hospital wastewater oxidation ponds discharge effluent onto Lunyangwa River, but data on its performance is scant. It was thus imperative to assess the performance in terms of levels of pH, EC, TDS, phosphates, feacal coliforms, biological oxygen demand (BOD5) and total suspended solids (TSS) removal from the influent. Grab water samples were collected from the influent, facultative pond, effluent and upper, point of discharge and downstream of the discharge point. Levels of temperature, pH, EC, TDS were determined on site using HANNA instrument model H19812 pH-EC-TDS meter. Levels of BOD5 were determined using DO meter. Feacal coliforms were determined using dilution method. Nitrates and phosphates were determined spectrophotometrically, whereas TSS was determined gravimetrically. Data was analysed using Minitab version 17. The removal efficiencies of TSS, TDS, E.coli, nitrates and EC were observed to be 46.67%, 59.43%, 96.23%, 6.34% and 59.34%, respectively. Except for E.coli, the performance of Mzuzu Central Hospital Wastewater Oxidation Ponds in removal of all parameter was generally low (i.e < 60%). In addition, the removal efficiencies of pH, temperature, PO43− and BOD were −23.19%, −4.35%, −20.65% and −69.23%, respectively, indicating that regardless of the weak wastewater (BOD5< 200 mg/L) of a raw wastewater collected, the performance of the oxidation is a challenge. Levels of BOD5, fecal coliform, phosphate, and pH, above Malawi Standards specifications for industrial effluents tolerance limits for Malawi in both the effluent and the receiving waters, were indicative of significant pollution resulting from the oxidation ponds, suggesting a pressing need for improvement in wastewater treatment in order to improve the water quality ratings prior to discharge into Lunyangwa River. There is also a dire need for risk communication and public sensitization with respect to the need to boil and filter the water prior to consumption for communities that rely on downstream of the discharge point as their drinking water sources.

Biopolishing sanitary landfill leachate via cultivation of lipid-rich Scenedesmus microalgae

Sanitary landfill leachate is a toxic effluent with a composition that can vary widely and biological treatment using microalgae represents a promising for bioremediation alternative. In this study, treated sanitary landfill leachate (TSLL) collected after undergoing secondary treatment (biological stabilization pond) was used for the cultivation of Scenedesmus sp. (Chlorophyceae). The TSLL was mixed with tap water to obtain different concentrations (0, 20, 40, 60, 80 and 100% TSLL) before microalgal cultivation aimed at maximizing the production of biomass and lipids. The best concentration for Scenedesmus sp. growth was 80% TSLL, resulting in biomass and lipid productivities of 420 and 36 mg L−1 d−1, respectively, high concentrations of oleic (C18:1) and palmitic (C16:0) fatty acids, and effective removal of nitrogen (NO3−, ∼69%) and phosphorus (PO3−1, 87%). In addition, Scenedesmus sp. removed metals (Al, Cd, Cu, Fe, Ni, Rb and Zn) from the 80% TSLL through biosorption, suggesting that microalga can be used to remediate wastewater that has high polluting capacity. The ability of Scenedesmus sp. to grow in TSLL with high nitrate and heavy metal contents, allows the simultaneously purification of wastewater and the production of a lipid-rich biomass. The proportion of C16-C18 fatty acids in this biomass makes it suitable for biodiesel production.

Nitrogen removal from summer to winter in a field pilot-scale multistage constructed wetland-pond system

A pilot-scale multistage constructed wetland-pond (MCWP) system with a "pre-ecological oxidation pond, two-stage horizontal subsurface flow constructed wetland (HSCW) and surface flow constructed wetland (SFCW) as the core and postsubmerged plant pond" as the process was used to treat actual polluted river water in the field, and the variation in nitrogen removal from summer to winter was investigated. The results showed that the average total nitrogen (TN) removal efficiency in the MCWP was approximately 40.74%. The significant positive correlation between the daily highest temperature and the TN removal efficiency of the whole system was fitted with a nonlinear curve (R2 = 0.7192). The TN removal load rate in the HSCWs was 2.7–3.7 times that in the SFCW. The SFCW, which had high-density plants (35 plants/m2), increased the proportion of nitrogen removed by plant harvesting and microbial function. The TN transformed by Iris pseudacorus L. accounted for 54.53% in the SFCW. Furthermore, bacteria completed the nitrogen cycle in the SFCW through a variety of nitrogen removal pathways. This research not only investigated the TN removal performance in an MCWP system but also made it possible to predict the TN removal efficiency according to the daily highest temperature from summer to winter in the field.

Diversity of Adult Caddisfly (Trichoptera) in Two Intermittent Streams During Dry Season in Phayao Province, Thailand

The effect of anthropogenic activities on natural intermittent stream and diversity of adult caddisfly were studied at the University of Phayao, Thailand. The caddisfly adults were collected monthly from 2 intermittent streams (the Huai Thub Chang and Huai Luang streams) from February to May 2015 (cool-dry to hot-dry season) using a black-light trap. Huai Thub Chang stream received wastewater from the oxidation pond, while Huai Luang stream was affected by an agricultural field of the university. Both streams are located in a deciduous forest. The 14 species of 7 families were collected and identified. Cheumatopsyche lucida (Hydropsychidae) and Leptocerus dirghachuka (Leptoceridae) were found in both streams. C. lucida was the most abundant species. Micrasema turbo, Amphipsyche meridiana, C. globosa, Diplectrona lavinia, Macrostemum dohrni, Marilia sumatrana, and Wormaldia relicta were found only in Huai Thub Chang stream, whereas C. dhanikari, Lepidostoma doligung and Chimarra toga were found only in Huai Luang stream. A high number of C. lucida in both streams from February to April reflected a drought effect on the emergence of the caddisflies. Huai Thub Chang stream had a higher diversity of Trichoptera species than Huai Luang stream because of the variety of substrate types which were suited for the larval stage, especially hydropsychids.

Biochemical and phylogenetic characterization of the wastewater tolerant Chlamydomonas biconvexa Embrapa|LBA40 strain cultivated in palm oil mill effluent.

The increasing demand for water, food and energy poses challenges for the world´s sustainability. Tropical palm oil is currently the major source of vegetable oil worldwide with a production that exceeds 55 million tons per year, while generating over 200 million tons of palm oil mill effluent (POME). It could potentially be used as a substrate for production of microalgal biomass though. In this study, the microalgal strain Chlamydomonas biconvexa Embrapa|LBA40, originally isolated from a sugarcane vinasse stabilization pond, was selected among 17 strains tested for growth in POME retrieved from anaerobic ponds of a palm oil industrial plant located within the Amazon rainforest region. During cultivation in POME, C. biconvexa Embrapa|LBA40 biomass productivity reached 190.60 mgDW • L-1 • d-1 using 15L airlift flat plate photobioreactors. Carbohydrates comprised the major fraction of algal biomass (31.96%), while the lipidic fraction reached up to 11.3% of dry mass. Reductions of 99% in ammonium and nitrite, as well as 98% reduction in phosphate present in POME were detected after 5 days of algal cultivation. This suggests that the aerobic pond stage, usually used in palm oil industrial plants to reduce POME inorganic load, could be substituted by high rate photobioreactors, significantly reducing the time and area requirements for wastewater treatment. In addition, the complete mitochondrial genome of C. biconvexa Embrapa|LBA40 strain was sequenced, revealing a compact mitogenome, with 15.98 kb in size, a total of 14 genes, of which 9 are protein coding genes. Phylogenetic analysis confirmed the strain taxonomic status within the Chlamydomonas genus, opening up opportunities for future genetic modification and molecular breeding programs in these species.

FEASIBILITY STUDY OF CONSTRUCTED WETLANDS FOR THE TREATMENT OF DAIRY EFFLUENTS

This work aimed at characterizing the effluent of a small dairy in terms of flow and physical-chemical composition and at assessing constructed wetland for its treatment. The dairy produced an effluent with an average flow of 2.81 m³.d ‑ ¹ and the following characteristics: 574-4155 mg.L ‑ ¹ of BDO; 1531-7912 mg.L ‑ ¹ of TSS; and 23-173 mg.L ‑ ¹ of TKN. Using median values of BOD, three treatment systems were designed: batch activated sludge (BAS) and waste stabilisation ponds (WSP), commonly applied for the treatment of dairy effluents; and constructed wetlands (CW) as an alternative system. In terms of area requirements based on the removal of BOD, the BAS system (2.1 m²) was more advantageous than CW (15.0 m²) and WSP (46.5 m²). However, considering the removal of TKN and TSS, the WC system showed to be an attractive option for the treatment of the effluent studied. Next, a new CW system was designed aiming at removing BOD, TSS and TKN. In this case, the limiting parameter was the TKN, and not the BOD as expected. The designed CW system presented satisfactory hydraulic retention time (HRT) when compared to ranges reported in the literature, even when minimum, mean and maximum concentrations of NTK were considered for the design, corroborating the robustness of CW systems. The findings of this study confirm, therefore, the wide variation of the characteristics of dairy effluents as well as the ability of CW systems to absorb such variations without compromising the efficiency of the treatment system.

A COMPREHENSIVE ASSESSMENT OF SEPTAGE MANAGEMENT IN BANTUL, YOGYAKARTA

Aim: This study aims to assess the entire process of septage management comprising regulation, operational procedures, finance, community involvement, and water quality analysis to maximize the initial and hugest human fecal sludge treatment called Faecal Sludge Treatment Plant (IPLT) in Yogyakarta. Methodology and Results: The Modified EHRA (Environmental Health Risk Assessment) method was applied which focused only on wastewater treatment aspect. Several regulations including standard quality methods (SNI) were utilized and made a comparison between baseline rules and obtained results. Furthermore, quality assessment was accomplished by observation and interview. The results showed that the human sector needs to improve not only the amount of operators but also urgently put up protective personal equipment during the suction process. The dissemination of attractive information about sludge suction service done by PUPKP as a representation of the local government among the dwellers ought to upgrade a lot. Technologies employed which are carriage transportation and vacuum machine, are good enough. Contrarily, septage treatment plants require extra-effort to enhance it as most water quality parameters barely meet the standard quality. BOD, COD, ammonia, total coliform, oil and grease do not meet the third class of water quality (Government Regulation of Republic of Indonesia No. 82/2001). Subsequently, the effectiveness of each unit i.e. anaerobic tank and stabilization ponds are under 50% and the loading rate has a maximum capacity of 87.5m3/day, and 60m3/day minimum capacity. Conclusion, significance and impact of study: Therefore, almost all aspects of septage management in Bantul Yogyakarta are required to improve

Assessment of performance of wastewater stabilization ponds using faecal indicator bacteria reduction efficiency in a tropical environment

Egerton University (EU) uses Wastewater Stabilization Ponds (WSPs) for wastewater treatment. An adjoining wetland with gravel bed substrate and freesurface flow meant to polish discharge before releasing into River Njoro is currently non-operational. The current study aimed at establishing the performance of WSPs in terms of concentration and reduction efficiencies of Faecal Indicator Bacteria (FIB); Total Coliforms (TC) and Escherichia coli (E. coli). Wastewater samples were collected weekly for one month from mid- November to mid-December 2017. Total Coliforms and E. coli were isolated using selective and differential media following Membrane Filtration (MF) method. Colonies were cultured on Chromocult Coliform Agar (CCA) and enumerated using standard procedures for examination of water and wastewater. The results were expressed as Colony Forming Units (CFUs) per 100 ml of the original sample. The inlet showed highest concentration of FIB which reduced along the treatment pathway. Total Coliforms and E. coli ranged between 2.5 × 108 - 2.9 × 1011 and 5.9 × 105 - 1.8 × 1010 CFUs/100 ml respectively with cumulative reduction efficiencies between 2 to 4 log units for E. coli and 2 to 3 log units for TC in the two maturation ponds. Although concentration of FIB in EU WSPs reduces along the treatment pathway, the effluent quality is above recommended international standards for discharge into surface waters. The trend is attributed to lack of frequent monitoring, insufficient maintenance, together with short- circuiting effect due to by-passing of wastewater in the design of the new pond system.

Alteration of antibiotic-resistant phenotypes and minimal inhibitory concentration of Escherichia coli in pig farming: Comparison between closed and open farming systems

The prevalence of antibiotic residues and antibiotic-resistant Escherichia coli (ARE) in closed (CSF) and open (OSF) pig farming systems was analysed. Results showed that a high level of E. coli populations, antibiotic contamination in supplied water, and additional antibiotics used, such as neomycin (NEO) or colistin (CLT), were observed in OSF. Similar ARE resistance to five antibiotics, including NEO, was observed in the water source, dung, and wastewater/sludge but were different from those of CLT. An increased occurrence of ARE was found in the sludge of anaerobic digestion (AD) and the waste stabilisation pond (WSP), but they were not well correlated with their residual antibiotic concentrations. CLT administration yielded higher ARE prevalence in pig excreta and wastewater in OSF, but its absence in CSF also resulted in ARE occurrence with increased minimal inhibitory concentration (MIC) levels in the anaerobic digester/waste stabilisation ponds. This study revealed that ARE prevalence and MIC levels of CLT could be developed during the wastewater treatment process in the pig farm, although none of the AREs were found in the original excreta/wastewater.

Temperature Stratification in an Operational Waste-Stabilization Pond

Waste stabilization ponds (WSPs) rely on natural processes to improve water quality. WSPs require less capital or operational resources than traditional treatment and are commonly used in rural communities or for secondary disinfection. Typically, WSPs designs use empirical equations without three-dimensional (3D) circulation, thermal stratification, or varying water levels. In the present study, a 3D numerical model (Delft3D version 4.04) was applied combined with observations of an operational WSP for nine months (May–November 2017). After calibrating light attenuation and eddy viscosity, model results were in agreement with temperature profiles at five locations, with an average root mean square errors of 1.3°C. The results indicate minimal effects from inflows temperatures and vertical temperature differences of up to 8.0°C between the surface and bed, which inhibited vertical mixing. The buoyancy frequency, a measure of density stratification, was inversely proportional to wind speed and was used to determine that the threshold wind speed required for mixing varied seasonally between 1 and 3 m/s. The results from a simulated tracer indicate that empirical methods for estimating hydraulic retention times—the average length of time water remains in a WSP—are inaccurate and varied by an average of 22% from the simulated tracer.

Migration mechanism and risk assessment of chlorinated paraffins in highly polluted Ya’Er lake area, China

Chlorinated paraffins (CPs), a type of toxic and persistent organic substances, can persist in environmental media for a long time and have adverse effects on human health. Thus, it is of great importance to investigate the accumulation and environmental behavior of CPs in industrial areas. In this study, farmland soil, water, and sediment core samples from abandoned oxidation ponds used by three chemical plants to treat wastewater over the past 38 years were investigated in detail. Results show that the concentration of CPs in sediments varied significantly with the water flow direction. The oxidation pond closest to a sewage outlet had the highest concentrations of short-chain chlorinated paraffin (SCCPs) and medium-chain chlorinated paraffin (MCCPs), within the ranges of 44.0–6.21 × 104 ng/g dw (mean 9.32 × 103 ng/g dw) and 143–1.30 × 106 ng/g dw (mean 1.22 × 105 ng/g dw), respectively. However, in the oxidation pond farthest from the sewage outlet, CP concentrations in sediments were significantly reduced, with ∑SCCPs and ∑MCCPs concentrations ranging from N.D.-249 ng/g dw (mean 66.8 ng/g dw) and N.D.-222 ng/g dw (mean 34.0 ng/g dw), respectively. Moreover, MCCP level in the water was below the detection limit, while the concentration of SCCP ranged from 41.0 to 1.53 × 103 ng/L (mean 267 ng/L). Finally, a remarkable spatial trend and specific congener distribution were observed in the sediment test results. The horizontal and vertical distributions of the sediments indicate that short-chain (C10-11) and low-chlorinated (Cl6-7) homologs are more likely to migrate deeper or farther away from the pollution source.