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    Performance optimization modelling of a horizontal roughing filter for the treatment of mixed greywater
    (2021-12-01) Mtsweni, Sphesihle; Rathilal, Sudesh; Bakare, Babatunde F.
    The growing demand of development of appropriate and relevant wastewater treatment technology is drastically increasing in rural and urban communities in many parts of the world including South Africa. This is largely exacerbated by the escalation of water demand and decreasing potable water availability. As a result, advanced research related to the development and optimization of water treatment technologies is becoming an urgent necessity including research focusing on wastewater recycling and reclamation. Meanwhile, horizontal roughing filter (HRF) technology is one such physical water pre-treatment system that can effectively and efficiently treat wastewater and thus reduce the reliance on potable water use. Therefore, this study aimed at modelling HRF in order to investigate the option of domestic greywater reuse for delivering desired water quality for nonpotable applications. The overall aim of the study was modelling the HRF in order to improve its performance and several objectives were investigated in this study. The first one was the characterization of biological and physico-chemical strength of greywater originated from kitchen, bath and laundry sources. The second objective investigated the HRF performance/efficiency after treating various domestic greywater pollutants. The third objective investigated the controlling factors affecting the performance and optimization of the HRF during its operation. This was investigated based on design of experiments (DOE) and response surface methodology (RSM). Based on the artificial neural network (ANN), the first objective investigated the filter duration in a HRF using ANN modelling for high level of contaminants in domestic greywater. Secondly, the ANN models applicable to a HRF were investigated and used for the prediction of greywater quality variables from the output stream of the HRF based on experimental data obtained from the operation of the HRF equipment. The first step in water treatment processes requires quality analysis in order to understand the constituent of water pollutants. Therefore, the experimental analysis of biological and physicochemical contents in greywater sources was conducted in this study. The next aspect involved treatment of mixed domestic greywater using a three compartment HRF unit which was fixed at a low filtration rate of 0.3 m/h. The effect of operating parameters on the HRF performance was studied factorial design and optimization. The factorial design application in HRF defines performance based on derivation of right factor settings for the effective operation of HRF. The aspect of ANN was undertaken to investigate the applicability, effectiveness and predictive ability of ANN within a HRF equipment. The use of ANN in HRF can serve as a monitoring tool in terms of performance and also as an indicator of any quality deviation that might be occurring during the filter operation. The key findings were obtained on qualitative analysis of domestic greywater originating from a peri-urban community for the quantification of biological and physico-chemical contaminants. The significant quality difference was recorded in greywater sources and the kitchen greywater source recorded the highest load of pollutants compared to the laundry and bathing sources at p<0.05 significant level. Furthermore, the quality difference was evident in greywater sources in terms of daily households’ social conditions, activities and practices. Also, the analysis of microbes in domestic greywater recorded high values of Escherichia coli (E. coli) and total coliform contamination which poses health related risks in domestic greywater reuse. Therefore, further treatment of domestic greywater prior to reuse remained necessary. The effectiveness of HRF was evident in removing biological and physico-chemical pollution load in domestic greywater at 0.3 m/h filtration rate. An average of 90% turbidity removal was obtained with 86% removal of conductivity and 84% of total solids and more than 50-70% removal of chemical oxygen demand (COD) within the HRF system. The E. coli and total coliforms were totally removed in the three compartment HRF. Based on DOE analysis, the significant factors identified were flowrate, gravel media, filter bed height and filter length and most significant contributing factor identified was filtration rate. Furthermore, the optimization of the HRF resulted in a high efficiency of 76% for the removal of turbidity. Results on ANN modelling for the prediction of turbidity of the effluent stream from the HRF showed good learning abilities of the ANN and the optimal ANN structure obtained was 4-7-1 structure using the trainlm algorithm. The mean square error (MSE) value below 10% was obtained after training and the R correlation coefficient >0.9 was obtained in training, testing, validation and all data sets. For the prediction of COD, the optimal ANN architecture was 3-10-1 which was obtained with trainlm training algorithm. A satisfactory mean absolute percentage error (MAPE), low mean absolute error (MAE) and high R correlation coefficients close to 1 for the training and testing sets were also recoded for this ANN model for the prediction of COD. The other objective was the investigation of filter duration in HRF using ANN and a 4-8-2 optimal structure was obtained with the trainlm algorithm which outperformed other training algorithms for the prediction of filter duration along with turbidity. Also, a high R correlation coefficient and low MSE value was obtained for this optimal ANN model for the predicted filter duration. For this model, satisfactory R correlation values for training, testing, validation and all data were close to 1. Results on feedforward multi-input multi-output (MIMO) ANN showed good accuracy in predicting multioutput parameters of domestic greywater effluent from the HRF. The optimal ANN architecture obtained through a trial-and-error approach for MIMO ANN was 7-15-4. During training, different structures of ANN were investigated through varying training functions, neurons and combination of physico-chemical parameters and learning functions. For the optimal ANN model, the MSE of 0.001 was finally obtained based on the training data set. Furthermore, the R correlation values above 0.9 for training, testing, validation and all data sets were obtained. The optimal ANN model also showed good prediction and satisfactory accuracy when a new set of sample data was presented to the network. Therefore, based on the objectives and findings of this study, the pollution load in domestic greywater characteristics can contain a number of pollutants and can significantly vary with greywater sources. It is also important to note that the HRF significantly showed effectiveness in treating physical pollutants and large amounts of chemical and biological pollutants. From the findings and based on the HRF, it was also noted that the chemical pollutants can be significantly removed using a combination of physical and chemical treatment processes in order to remove more pollutants. This was observed by a high removal of physical pollutants such as turbidity, conductivity and solids while domestic greywater biodegradability ratio was lower than 0.5. Furthermore, for the DOE/RSM techniques, it was also observed that the effective filter performance of the HRF is a function of multi-design parameters such as filtration rate, filter length, gravel media and bed height and multi factor optimization was useful in this research work. Finally, the ANN showed effective characteristics and accuracy in the HRF equipment for the prediction of multi-output variables of the effluent greywater from the HRF following mixed domestic greywater pre-treatment.
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    Characteristics of greywater from different sources within households in a community in Durban, South Africa
    (IWA Publishing, 2017) Bakare, Babatunde F.; Mtsweni, Sphesihle; Rathilal, Sudesh
    The reuse of greywater is steadily gaining importance in South Africa. Greywater contains pollutants that could have adverse effects on the environment and public health if the water is not treated before reuse. Successful implementation of any greywater treatment process depends largely on its characteristics in terms of the pollutant strength. This study investigated the physico-chemical characteristics of greywater from different sources within 75 households in a community in Durban, South Africa. The study was undertaken to create an understanding of greywater quality from different sources within and between households. Greywater samples were collected from the kitchen, laundry and bathing facilities within each of the households. The samples were analysed for: pH, conductivity, turbidity, total solids, chemical oxygen demand (COD) and biological oxygen demand (BOD). There was a significant difference in the parameters analysed between the greywater from the kitchen compared with the greywater from the bathtub/shower and laundry. It was also observed that the characteristics of greywater from the different households varied considerably. The characteristics of the greywater obtained in this study suggest that the greywater generated cannot be easily treatable using biological treatment processes and/or technologies due to the very low mean BOD : COD ratio (<0.5).
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    A pilot study into public attitudes and perceptions towards greywater reuse in a low cost housing development in Durban, South Africa
    (IWA Publishing, 2016) Bakare, Babatunde F.; Mtsweni, Sphesihle; Rathilal, Sudesh
    The benefits of greywater reuse have been identified to include the protection of water resources, recovery of nutrients for agriculture, savings in fresh water usage, reduction in volumes of wastewater discharged into wastewater treatment works, groundwater recharge and sustainable water resource management. An understanding of public attitude and perceptions towards the reuse of greywater will help to facilitate a positive reaction to the promotion of such concepts. The study involved administering of structured questionnaires to residents within the community through field visits. The questionnaire addressed issues related to attitudes towards the reuse of greywater, perceived advantages related to the reuse of greywater and concerns related to public health issues regarding the reuse of greywater. A total number of 346 questionnaires were administered and respondents were aged from less than 19 to over 60 years. Of the respondents, 55% were female and 45% male. The findings revealed a complex and shifting relationship between attitudes towards and perception of the reuse of greywater. This paper thus presents the findings and assesses certain aspects of greywater reuse.
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    Performance of a horizontal roughing filtration system for the pretreatment of greywater
    (2016) Mtsweni, Sphesihle; Rathilal, Sudesh; Bakare, Babatunde F.
    A large fraction of the world's population, around 1.1 billion people, do not have access to acceptable sources of water. In South Africa there is a growing pressure on the available freshwater resources. New sources of freshwater supply are becoming increasingly scarce, expensive or politically controversial. This has led to large scale interest in the application of water reclamation and reuse of domestic, mining and industrial wastewater as an alternative water supply sources. This is becoming critical to sustain development and economic growth in the Southern African region. This research aims at providing both social and scientific information on the importance of greywater reuse and recycling as an alternate source to aid water demand management under South African conditions. The approach to this research work was divided into two main thrusts: the first was to gain an understanding of the public attitudes towards the idea of reusing greywater that is usually perceived as wastewater which pose health concerns. The second was to provide an understanding of typical greywater quality in a peri-urban community in Durban, South Africa as well as investigate the suitability of a horizontal roughing filtration system in reducing pollutant strength of contaminants found in greywater for non-potable reuse applications. In order to achieve the central aim of this research study, the following objectives were considered: • Investigation of public perception and attitudes towards the reuse of greywater. • Determination of greywater quality in a peri-urban community in Durban South Africa. • Investigation of the performance of a horizontal roughing filtration system for the treatment of greywater collected from a peri-urban community in Durban, South Africa. It was important to have an understanding of public perception and attitudes towards the reuse of greywater because of the fact that the success of any reuse application depends on the acceptance of the public. The methodological approach for this aspect of the research work involved administering of structured questionnaires to residents within the community through field visits. The questionnaire addressed issues related to attitudes towards the reuse of greywater, perceived advantages related to the reuse of greywater and concerns related to public health issues regarding the reuse of greywater. The successful implementation of any greywater treatment process depends largely on its characteristics in terms of the pollutant strength. The methodological approach for this aspect of the research work involved physico- chemical characterization of the greywater collected from different sources within the households in the peri-urban community. Greywater samples were collected from the kitchen, shower and laundry within each of the households. This aspect of the research work was undertaken to gain an understanding of greywater quality from different sources within and between households. In order to achieve the third objective of this research work, a pilot plant horizontal roughing filtration system was designed and fabricated for the treatment of greywater. The system consisted of three compartments containing different sizes of gravel that served as the filter media. This was done in order to investigate the effect of varying filter media size on the performance of the horizontal roughing filtration system in treating greywater. The system had an adjustable manual valve used in varying the filtration rate. The impact of varying filtration rate on the performance of the horizontal roughing filtration system in treating greywater was also investigated. The main findings of this research were: • From the survey conducted, the percentage of the public willing to accept the reuse of greywater within the community was far higher than the percentage opposing its reuse. Concerns have often been expressed by the public that the reuse of greywater could pose possible adverse effects to public health. However, in this pilot study it was found that a higher percentage of respondents (>60%) disagree that the reuse of greywater could negatively impact on public health compared to less than 20% of the respondents that agree. An interesting finding of this study was that a greater percentage of the respondents were willing to have a dual water distribution system installed in their current place of residence. • The physico-chemical characterization of greywater from different sources within the households investigated indicated that, the quality of greywater varies considerably between all sources and from household to household. None of the households investigated produced the same quality of greywater. It was also found that greywater generated from the kitchen contains the most significant pollutants in terms of the physico-chemical parameters considered in this study compared to the other sources within the household. • The pilot plant horizontal roughing filtration system demonstrated its suitability for the treatment of greywater for non-potable reuse applications. It was observed that 90% turbidity and 63% Chemical Oxygen Demand reduction was achieved over the entire duration of operation of the horizontal roughing filter. It was also observed that the removal efficiency was significantly higher in the compartment with the smallest filter media size and the removal efficiency was significantly higher at lower filtration rates. It is therefore concluded from the investigation conducted in this research that the role of the public is a vital component in the development and implementation of any reuse system / application. It was found that there was a relatively high level of acceptance for the reuse of greywater among the respondents within the community where the study was conducted. The greywater characteristics results obtained from this investigation indicated the necessity of treatment prior to disposal in the environment. Also, a low BOD5/COD ratio of 0.24, which is significantly lower than 0.5, is an indication that the greywater generated from the community cannot be easily treated using biological treatment processes and/or technologies. The pilot horizontal roughing filtration system used for the treatment of greywater in this study demonstrated its suitability for the treatment of greywater for non-potable reuse applications such as irrigation, toilet flushing and washing activities.