Rural Wastewater Research Articles

Measurement and simulation of dissolved oxygen in Zayandehrood river

Aims: This study aims to simulate dissolved oxygen of Zayandehrood river from regulating dam to Polle-Kalleh bridge using MIKE11 software that is a hydrodynamics and water quality model. Materials and Methods: During 5 months the samples were taken from four hydrometric stations and water quality parameters such as dissolved oxygen, pH, BOD (1 day, 3 days, 5 days, and 7 days), NH 4 , NO 3 - phosphate (PO4 3- ), and temperature were measured. Morphological and hydrological data were provided and introduced into the model. The model was calibrated and its accuracy was investigated. Results: The results indicated that concentration of PO4 3- , BOD5 , COD, NH 4 , and NO3 - exceeded surface water standards from regulating dam to Pole-Kalleh bridge. The results of the prediction for the next 25 years indicated that due to growth of population and industries along the river, concentration of some pollutants will be increased. Conclusions: The results indicated that although the current DO level is suitable for aquatic environment, this is not adequate for fish reproduction and migration. Prediction of the river water quality parameters for the future conditions showed that discharge of urban and rural wastewater to river should be avoided. In situations where release of effluent into the river is inevitable, nitrification process should be added to wastewater treatment processes.

Evaluation of rural wastewater treatment processes in a county of eastern China

With the rapid urbanization and industrialization in China, wastewater treatment in rural areas has become an increasing national concern. The selection of appropriate treatment processes closely based on the actual local status is crucial for the prevention of water quality deterioration in rural areas of China. This study presents a full year survey on the performances of various rural wastewater treatment processes at a county level in eastern China including seven three-chamber septic tanks (ST), five micro-power biological facilities (MP), seven constructed wetlands (CW), three stabilization ponds (SP) and five centralized activated sludge treatment plants (AS). It was found that although ST could remove a notable portion of total suspended solids (TSS) and chemical oxygen demand (COD(Cr)), it was ineffective in reducing nutrients and pathogens. Reliability and stability analyses showed that the centralized AS and decentralized CW processes outperformed the SP and MP processes. There were obvious discrepancies between the mean design concentrations, which ensure that 95% of the effluents meet the discharge standards, and the actual effluent concentrations determined for each process. The expected compliance with the tentatively adopted second-grade discharge standards (GB 18918-2002) was unsatisfactory for most of the water quality parameters examined, indicating an urgent need to design more practical discharge standards for decentralized treatment processes. Based on an overall assessment of reliability, stability and cost-effectiveness, the centralized AS was suitable for densely populated towns while the decentralized CW was suitable for sparsely populated villages.

Experiment on the Treatment of the Rural Wastewater by the Paddy Wetland System

A field experiment was conducted to remove the potential eutrophication effect of N and P from rural wastewater (RW) during the whole rice growing season of 2010. Commercial fertilizer and RW were applied to furnish 40 kg P ha-1except CK. Results showed TN concentration of the floodwater in the paddy wetland system decreased quickly after transplanting, rosed significantly (P ≤ 0.05) after two N topdressings, and then decreased gradually as the following sequences: SW > GW > DW > BW > CK. Total P (TP) concentration had significantly declined after P application, from October 15 there were no significant increases in TP concentration in the floodwater. Meanwhile, the yield for CK was significantly less (P ≤0.05) than SW, GW, DW, and BW, with the yield of BW significantly greater (P ≤ 0.05) than other treatments. It is feasible to remove N and P from RW by the paddy wetland system and can be widely used to improve the yield of rice.

Study on Anoxic / Anaerobic / Aerobic Process to Treat Rural Domestic Wastewater

The anoxic, anaerobic and aerobic reactors were used to treat rural domestic wastewater, single-stage reactor inoculated with different sludge was optimized, and the removal efficiencies of CODCr and TP were discussed. The results indicated that the anoxic and anaerobic reactors inoculated with anaerobic sludge could be selected as the effective unit for the anoxic/anaerobic /aerobic process. The removal efficiency of CODCr could reach 95.1%, the effluent CODCr was 25.7mg/L~97.2mg/L, the removal efficiency of TP could reach 97.1%, the effluent TP was 0.24mg/L~0.96mg/L.

Study of a Novel Vertical Flow Constructed Wetland System with Drop Aeration for Rural Wastewater Treatment

Constructed wetlands are recognized as a reliable technology for rural wastewater treatment. However, conventional constructed wetlands face problems with low pollutant removal efficiency and limited oxygen transfer capability. Therefore, a novel vertical flow constructed wetland (VFCW) system with drop aeration was developed in this study. Two pilot-scale vertical flow constructed wetlands of 0.75 m2 each were constructed with the same dimensions and configuration but different media, one of which (named as CW1) was filled with a 1:1 mixture (by weight) of zeolite and dolomite and the other (named as CW2) with the same zeolite only. The oxygen transfer capability of a multilevel two-layer drop aeration device, organics and nitrogen removal of CW1 and CW2, and pollutant distribution along the depths of CW1 and CW2 in different operational phases were studied. The results demonstrated that compared with the direct drop aeration process, the multilevel, two-layer drop aeration device supplied 2–6 mg/L higher dissolved oxygen per meter of drop height, and after installation of the six-level, two-layer drop aeration devices, the 5-day biochemical oxygen demand removal load was improved from 8.1 to 14.2 g m−2 day−1 for CW1. With regard to the different filter media, nitrogen removal was improved by the adsorption of zeolite in the first year, with 5–36% higher NH 4 + –N removal efficiency of CW2 compared with that in CW1. Since it did not have a significant positive effect on phosphate removal, dolomite can be replaced by zeolite. The chemical oxygen demand removal mainly took place in the upper 15-cm filter layer in different operational phases, while nitrogen distribution along the depths of the VFCWs was different in different operational phases. In addition, as no operational problems occurred, the vertical flow constructed wetland system with drop aeration is an appropriate alternative for rural wastewater treatment, with numerous advantages of low capital and operation costs, no energy consumption, easy maintenance, high hydraulic loading rate, high pollutant removal efficiency, and no clogging.

Evaluation of the performance of rural wastewater treatment plants using chemical measurements in combination with statistical techniques: a case study

The performance of a wastewater treatment plant was assessed statistically using multivariate cluster and principle component analysis. This was after measuring some physico-chemical properties in the influent, effluent, downstream, and upstream waters over a 4-month period. The cluster analysis grouped the sampling sites into three clusters: relatively non-polluted (upstream), medium polluted (downstream), and polluted (influent and effluent). The polluted water was further subdivided into very highly (influent) and highly (effluent) polluted. The grouping of influent and effluent into one cluster was due to some water quality parameters such as amount of copper, lead, and phosphates that are not efficiently removed by the plant. Using principal component analysis, samples from the same site taken over a period of 4 months were scattered, indicating inconsistencies in the performance of the plant. This was more pronounced during the rainy season, suggesting that increased water volumes from open sewers make the already poorly performing plant worse. The major loading factors found by principle component analysis were phosphate, lead, iron, zinc, copper, pH, and conductivity. Generally, the wastewater treatment system was found to be efficient in removing heavy metals and these were found in the sludge, but not anions. The mean percentage metal removal could be arranged in the following decreasing order: iron (85%) > zinc (57%) > copper (40%) and lead (38%) following the concentrations (mg kg−1) found in the sludge: iron (11,300) > zinc (820) > copper (180) > lead (20) > cadmium (3). Phosphate and iron concentrations in the effluent were found to be above the South African Bureau of Standards (SABS) recommendations. The major cause of poor performance is the high volume of the wastewater, exceeding the capacity of the plant 10 times.

Pyrolysed powdered mussel shells for eutrophication control: effect of particle size and powder concentration on the mechanism and extent of phosphate removal

AbstractThe international shellfish farming industry has a growing problem with respect to sustainability: the shells, a by‐product, are currently being mostly wasted to landfill. Instead, this calcium‐rich resource can be used to produce lime [calcium oxide (CaO)] and then used to remove phosphate from rural wastewaters. Powdered mussel shell was heat treated to form lime. Two different shell particle sizes (fine, 53–106 µm; coarse, 212–250 µm) as well as various pyrolysis times, heating rates, pyrolysis temperatures and shell concentrations were used to determine the effects of these parameters on the lime formation and subsequent phosphate removal from a synthetic wastewater. Furthermore, the mechanisms of phosphate removal were determined by quantifying the phosphate content in all components before and after reaction with the synthetic wastewater. It was found that with excess of partially calcined pyrolysed shells, at a concentration of 5 g l−1, more than 95% phosphate removal was achieved, irrespective of particle size or pyrolysis conditions. When using optimally heat‐treated shells (particle size: 53–106 µm, pyrolysed for 1 h at 750 °C), it was possible to achieve over 90% phosphate removal using just 196 mg l−1 of shell. For the pyrolysed shells, the main mechanisms of phosphate removal were homogeneous nucleation to form a suspended precipitate, as well as adsorption and heterogeneous precipitation on the surface of the remaining calcite shell particles. Copyright © 2010 Curtin University of Technology and John Wiley & Sons, Ltd.

Sustainable Sanitation as a Part of an IWRM in the Karst Area of Gunung Kidul: Community Acceptance and Opinion

To overcome the problem of water scarcity in a rural karst area located in Gunung Sewu, Yogyakarta, Indonesia, water from an underground cave (Bribin Cave) is pumped and distributed to the people. Since karst aquifers are often considered as highly vulnerable to contamination from human activities, potential problems caused by current sanitation and hygiene practices in the recharge region must be anticipated. About 90% of the people in the recharge area use pour flush syphon toilets with poorly designed septic tanks and the rest have simple pit latrines. However, the existing septic tanks are very poorly designed and are actually only improved infiltration pits. One possible option to reduce the risk of aquifer contamination is to promote sustainable sanitation, which combines hygienic aspects with recycling of nutrients from human feces and urine. Sustainable sanitation comprises different technologies including low cost technology, which can be afforded by the community and provide economic benefit to the low income inhabitants in Gunung Sewu. The technology proposed is urine diverting and composting toilets. This paper presents the existing condition of rural domestic wastewater treatment and the opinion/ acceptance of the community in karst area of Gunung Sewu towards urine diverting and composting toilets. The results of the survey shows that although the acceptance of using the composting toilet is not high (25% to 43%), the interest of the community in using the end product is relatively high. While the acceptance of composting fertilizer from feces (humanure) ranges from 37% to 57%, urine fertilizer attracts 42%-71% respondents' interest.

Performance of Surface-Flow Domestic Wastewater Treatment Wetlands

Treatment wetlands can be a viable alternative for rural wastewater treatment where conventional centralized methods of treatment may not be feasible. The seasonal treatment performance associated with two surface-flow domestic wastewater treatment wetlands located at the Bio-Environmental Engineering Centre in Truro, Nova Scotia was investigated between October 2007 and April 2009. Each wetland had a surface area of ≈ 100 m2, was loaded with ≈ 1,400 L of domestic septic tank effluent d−1, and had a theoretical hydraulic retention time (HRT) of ≈ 25 d. The wetlands achieved average% reductions on a concentration basis of 95% E. coli, 69% BOD5, 78% TSS, 46% TKN, 42% NH3, 39% TP, and 34% SRP. Average% mass reductions based on monthly flows were 92% E. coli, 59% BOD5, 65% of TSS, 23% TKN, 21% NH3, 8% TP, and 2% SRP. First order removal rate constants averaged 0.19 d−1 for E. coli, 0.08 d−1 TSS, 0.07 d−1 BOD5, 0.03 d−1 TKN, 0.04 d−1 NH3, and 0.03 d-1 for both TP and SRP. Treatment performance was highly variable and appeared to decrease over time. Seasonal variability, hydrologic loading, and long term performance must be considered during the design stage to ensure adequate treatment capacity.

Enhanced removal of organic matter and ammonia nitrogen in a one‐stage vertical flow constructed wetland system

AbstractA modified cyclic batch constructed wetland was innovated to examine the removal of organic matter and ammonia nitrogen from rural wastewater in the eastern area of China. The results demonstrated that mean percentage removal of BOD5 and NH‐N in the modified cyclic batch constructed wetland treating rural wastewater were 80 and 97%, respectively. Compared with conventional constructed wetland systems, the quality of effluent from the modified cyclic batch constructed wetland was higher when treating rural wastewater. The predominant process for BOD5 removal was aerobic biodegradation and biomass assimilation in the system, which accounted for more than 99% of total removal. Mass balance calculation of NH‐N showed that the average rate of nitrification was 6.247 g m−2 day−1, which was 7.5 times more than the amount removed by biomass assimilation. The supply of oxygen by the modified methods in the modified cyclic batch constructed wetland was significantly high for available oxygen, which was 76.984 g m−2 day−1, much higher than the demand for rural wastewater treatment. © 2009 American Institute of Chemical Engineers Environ Prog, 2010

Evaluation of phosphorus removal from wastewater by soils in rural areas in China

Low-cost, easy-maintenance and high-efficiency decentralized wastewater treatment technologies are urgently needed in rural areas of China. Processes with high potential for phosphorus removal are of great interest. However, commonly used treatment methods often do not meet the strict criteria for removing phosphorus from rural wastewater. In order to search an economic and simple technology for phosphorus removal from the common bio-technologies effluent, seven soil types collected from different rural areas in China were investigated for their ability to remove phosphorus. X-ray diffraction (XRD) was used to analyse the mineral structure, and inductively coupled plasma optical emission spectrometer (ICP-OES) was used to analyse the geochemical composition of the soil samples. Three primary minerals – quartz, albite and montmorillonite – were clearly detected. The samples were divided into two soil types, acidic soils and alkaline soils, based on their pH values. The geochemical composition study indicated that a higher percentage of Ca and Mg occurred in alkaline soils (pH > 8) than in acidic soils (pH > 6.5). Adsorption isotherms from batch experiments fitted the Langmuir and Freundlich models well, the maximum P adsorption capacities ranged from 0.256 to 1.598 mg P/g, indicating a high phosphorus removal potential for all of these soils. The P fractions extracted revealed that the sum of NaOH-extracted inorganic P (NaOH-Pi) was the major P component in the acidic soils, and CaCO 3-bound phosphorus (Ca-P) in the alkaline soils. Dynamic adsorption simulation showed that these soils have the ability to remove phosphorus from wastewater.

Prevalence and distribution of Listeria pathogens in the final effluents of a rural wastewater treatment facility in the Eastern Cape Province of South Africa

We assessed the prevalence of free-living and plankton-associated Listeria species in the final effluents of a South African wastewater treatment facility and its receiving watershed between August 2007 and July 2008 as well as the antibiotic susceptibilities of effluent isolates. The physicochemical quality of the raw sewage and treated effluents was also determined. Free-living Listeria were more prevalent (96%), compared to plankton-associated Listeria species (58–67%). Listeria pathogens were sensitive to 11 (55%) of the 20 tested antibiotics, and showed varying (7–71%) levels of resistance to eight antibiotics. Turbidity, COD, NO3, PO4 and Listeria density fell short of recommended standards after treatment; while pH, temperature, TDS, DO and NO2 were compliant with target quality after treatment. We conclude that final effluents of wastewater treatment plants are potential sources of Listeria pathogens in the aquatic milieu of South Africa.

Occurrence of potentially pathogenic vibrios in final effluents of a wastewater treatment facility in a rural community of the Eastern Cape Province of South Africa

We assessed the occurrence of Vibrio pathogens in the final effluents of a rural wastewater treatment facility in the Eastern Cape Province of South Africa as free or plankton-associated (180 μm, 60 μm and 20 μm plankton sizes) entities using standard culture-based and molecular techniques. The free-living Vibrio densities varied from 0 to 3.45 × 101 cfu ml−1, while the plankton-associated Vibrio densities vary with plankton sizes as follows: 180 μm (0–4.50 × 103 cfu ml−1); 60 μm (0–4.86 × 103 cfu ml−1); 20 μm (0–1.9 × 105 cfu ml−1). The seasonal variations in the Vibrio densities in the 180 and 60 μm plankton size samples were significant (p < 0.05), while the 20 μm plankton size and free-living Vibrio densities were not. Molecular confirmation of the presumptive vibrios isolates revealed fluvialis (36.5%), as the predominant species, followed by Vibrio vulnificus (34.6%), and Vibrio parahaemolyticus (23.1%); only API 20NE was employed to detect Vibrio metschnikovii (5.8%), suggesting a high incidence of pathogenic Vibrio species in the final effluent of the rural wastewater facility. Analysis suggested that the concentration of Vibrio species correlated negatively with salinity and temperature (p < 0.001 and p < 0.002 respectively) as well as with pH and turbidity (p < 0.001) in the final effluent. We conclude that rural wastewater treatment facilities in the Eastern Cape Province of South Africa are potential sources of Vibrio pathogens in the aquatic environment of the communities.

Phosphorus removal of rural wastewater by the paddy-rice-wetland system in Tai Lake Basin

A field experiment was conducted to remove the potential eutrophication effect of P from rural wastewater (RW) during the whole rice growing season of 2007. The experiments consisted of five treatments, namely black water (BW), domestic wastewater (DW), grey water (GW), surface lake water (SW) and surface lake water without P application as a check (CK), with three replicates in a randomized block design. Commercial fertilizer and RW were applied to furnish 40 kg Pha(-1) except CK. Results showed total P (TP) concentration had significantly declined after P application, from October 15 there were no significant increases in TP concentration in the floodwater. TP removal rates from RW was significantly higher (P<or=0.05) than those from fertilizer. TP load was in an overall gradual decline, whereupon it became approximately steady on October 1. The percentage of TP load from wastewater decreased, whereas that from fertilizer continued to increase. Meanwhile, the yield for CK was significantly less (P<or=0.05) than SW, GW, DW, and BW, with the yield of BW significantly greater (P<or=0.05) than other treatments. It is feasible to remove P from RW by the paddy-rice-wetland system and can be widely used to improve the yield of rice.

Rural wastewater irrigation and nitrogen removal by the paddy wetland system in the Tai Lake region of China

Rural wastewater irrigation and nitrogen removal by the paddy wetland system in the Tai Lake region of China

Biofilm/membrane filtration for reclamation and reuse of rural wastewaters

To cost-effectively meet water quality and quantity requirements for rural areas, the objective of this research was to evaluate the performances of a three-stage process of anaerobic-oxic-anoxic biofilm filtration (AOBF) and membrane filtration (MF) processes and to assess the potential for reclamation and reuse of blended wastewater contained domestic wastewater, black water, and landfill leachate. The AOBF process at < LV 30 m/day showed good removal results of > 90% for conventional pollutants (> 75% for COD) and > 70% for nutrient. Influent step-feeding with 0.8Q into filter bed 1 and 0.2Q into filter bed 2 achieved denitrification efficiency of 5-10% higher than without step feed. Efficiencies of plate membrane removal were greater than 90% for COD and more than approximate 75% for nutrients and heavy metals, respectively. The AOBF/MF system showed excellent removal results of > 90-95% for soluble nutrients as well as nonsoluble fractions such as TSS, particulate COD. The effluent of AOBF/MF system met the reuse standard for industrial and agricultural water, while effluent of AOBF met the standard for the effluent quality of wastewater treatment plants. These results indicate that the AOBF/MF system was suitable for rural integrated wastewater treatment by achieving cost-effectively an effluent quality able to be used for industrial, agricultural and water bodies recharge purposes.

Simultaneous nitrification and denitrification in non-planted pilot-scale modified vertical flow constructed wetland systemA paper submitted to the Journal of Environmental Engineering and Science.

Rural wastewater containing low chemical oxygen demand (COD), but relatively high concentration of total nitrogen comprised of dominant ammonia-nitrogen, was treated in two vertical flow wetland systems whose effluent were discharged intermittently. A substantial loss of total nitrogen (30.3%) was found in a modified wetland system, which introduced an air pipe to enhance oxygen transfer, whereas only a minor loss (17.9%) in the conventional wetland. The correlation between pH, nitrite and nitrate concentrations, ammonia-nitrogen and nitrate-nitrogen distribution along with the depth in the wetlands indicated that the removal of total nitrogen did not follow the classic nitrification and denitrification pathway in the modified wetland system. Through mass balance calculation and theoretical analysis, it was found that simultaneous nitrification and denitrification (SND) was responsible for the transformation of soluble nitrogen into gaseous nitrogen in the modified wetland, thereby causing the loss of total nitrogen. The results showed that SND can be stimulated in aerobic wetland systems and its occurrence may depend on the biofilm thickness, the hydraulic detention time, and the type and population of microorganisms present in the wetland systems.

Improvement of nutrient removal and phosphorus recovery in the anaerobic/oxic/anoxic process combined with sludge ozonation and phosphorus adsorption

The effects of ozonation conditions on the performance of a continuous anaerobic/oxic/anoxic (A/O/A) process with sludge ozonation and phosphorus adsorption were investigated. In this system, excess sludge was ozonated by microbubble ozonation, and then the supernatant of the ozonated sludge was flowed into a phosphorus adsorption column packed with zirconium-ferrite adsorbent. The effluent from the column and the settlings of the ozonated sludge were recirculated in the A/O/A process. Long-term operation of a lab-scale system treating rural wastewater showed that ozonation affected not only the sludge reduction efficiency but also the nitrogen removal efficiency. When the amount of sludge to be ozonated was set at 16% of total MLSS per day, no excess sludge was withdrawn, but the nitrogen removal efficiency was deteriorated. Decreasing the amount of sludge to be ozonated (to 9.4% of total MLSS per day) resulted in efficient nitrogen removal, but the MLSS concentration increased slightly. Phosphorus accumulated in the sludge was re-solubilized by ozonation, and a large part of the solubilized phosphorus consisted of Pi. Almost all Pi was recovered in the phosphorus adsorption column.

Optimal Siting of Regional Fecal Sludge Treatment Facilities: St. Elizabeth, Jamaica

In the developing nation of Jamaica, 70% of the population depends upon on-site sanitation systems, which can provide an effective and low-cost option for rural wastewater treatment. However, there are serious environmental and human health effects associ- ated with their mismanagement and deterioration. Historically, fecal sludge management has been addressed as a localized problem. Instead, we introduce a regional decision model of FS treatment options. The problem is formulated as a mixed-integer programming model, which selects the optimal combination of treatment, hauling, and pumping options and their locations based on a variety of social and economic constraints. The constraint method of optimization led to an optimal trade-off curve between the number of people negatively affected and the cost of a given management plan. A sensitivity analysis documents model sensitivity to capital cost variation among potential treatment sites.

Defining and Managing Odors at a Previously Rural Wastewater Treatment Plant

Defining and Managing Odors at a Previously Rural Wastewater Treatment Plant