Theses and dissertations (Engineering and Built Environment)

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Aerobic sequencing batch reactor for the treatment of industrial wastewater from the brewery
(2017) Shabangu, Khaya Pearlman; Chetty, Maggie; Bakare, Babatunde F.
One of the major effects of socio-economic change due to industrialisation is the generation of industrial wastewater, which requires treatment before being released into the environment. Laboratory-scale aerobic sequencing batch reactors under suspended-growth heterotrophic activated sludge were operated in different aeration configurations to study their effect on the treatment of wastewater generated by a local brewery. The main purpose of this study was to evaluate the performance of the two laboratory-scale aerobic sequencing batch reactors treating brewery wastewater under continuous low-oxygen dosing concentration and cyclic aeration schemes on SBR operation. The characterisation of brewery wastewater was undertaken to assess the physicochemical composition of the wastewater produced from one of the breweries in South Africa (SAB). The data showed distinctive characteristics of brewery wastewater, which coincided with studies previously carried out on characterisation of brewery wastewater. The COD average concentration of the brewery influent was 7100 mg/L, with average pH values of 7. The BOD and the total solids content of the brewery wastewater influent from the facility were both high, implying that the influent was very rich in organic content and its discharge into water-receiving bodies or the municipal treatment plant could have adverse effects. From these results, a need for a competitive treatment technology was clearly highlighted so as to carry out a feasible treatment of the influent for the brewery industry. The aerobic sequencing batch reactors were designed, fabricated and set up for laboratory-scale treatment of wastewater from the brewery for 15 weeks. The performance of the two SBR configurations was determined with reference to COD, BOD, TS, VS and TSS. The experimental results demonstrated that wastewater generated from the breweries can be treated successfully using both aeration configurations. The results obtained indicated that treatment efficiencies in terms of COD and BOD were 94 % and 85 % respectively, for the reactor operated under continuous aeration configuration, while 81 % and 65 % was achieved for the reactor operated in the cyclic aeration scheme. The findings from this study demonstrate that the performance of the reactor operated under the continuous aeration scheme was successful, and showed statistically significant differences from the performance of the reactor operated under cyclic aeration schemes. These findings imply that there is a potential for the equipment, including financial benefit as a result of operating aerobic sequencing batch reactors for treating brewery wastewater under continuous low-oxygen concentration dosing schemes. In this study, it was also established that the maximum COD removal could be reached at an optimum hydraulic retention times of 5 days for both reactors. This was based upon viewing the experimental data; it appeared that the most significant difference in percentage COD removal was for HRTs 3 days and 4 days. Although, due to less percentage COD removal observed from HRTs 5 days till 7 days, it was hence established that the optimum removal of high strength organics in the brewery wastewater could be achieved within 5 days of treatment time. The pH adapted at an average of 7 for all batch experimentations of the study. The temperature maintained an average of 23 oC ambient, throughout the experimental period. These physical parameters ensured that the microbial population was kept healthy, without inhibiting its biological degradation activity. Although, sludge build up was observed in both aerobic SBRs on completion of each batch operation due to solids retention and organic pollutants biodegradation from the brewery wastewater. It was perceived that frequently reseeding both aerobic SBRs, as an alternative to 28 days sludge retention time would enhance the recovery of biomass, thus improving the overall removal of TSS consequently minimising sludge bulking in both reactors.
Biological nutrient removal from industrial wastewater using a sequencing batch reactor
(2018) Khumalo, Siphesihle Mangena; Bakare, Babatunde F.
South Africa is not an exception when it comes to the issue of fresh water scarcity perpetuated by environmental pollution among many other factors. Industrial wastewater particularly emanating from the brewing industry, contains high-strength organic, inorganic, and biological compounds which are toxic to the environment. Due to stringent industrial effluent dewatering standards enforced by both local and international environmental protection entities, industrial wastewater cannot be discharged into receiving water bodies prior to treatment. The overall aim of this study was to evaluate the performance or treatment efficacy of a laboratory scale sequencing batch reactor on biological nutrient removal using industrial wastewater from brewery. In this study, two laboratory scale sequencing batch reactors (SBRs) operated in a cyclic aerobic-anaerobic configuration inoculated with activated sludge were investigated for their removal of orthophosphates and nitrogen compounds from brewery wastewater. SBR-1 was investigated for nitrogen group pollutant removal and SBR-2 was investigated for orthophosphate removal. The findings of the study are reported based on overall removal efficacies for the following process monitoring parameters: orthophosphates, ammoniacal nitrogen, total Kjeldahl nitrogen, total nitrogen, total organic nitrogen, total inorganic nitrogen and NO3-N+NO2-N. From the investigation, the following overall removal efficacies were obtained: 69% orthophosphates, 69% ammoniacal nitrogen, 59% total Kjeldahl nitrogen, 60% total nitrogen, 64% total organic nitrogen, 67% total inorganic nitrogen and 56% NO3-N+NO2-N at an organic loading rate of 3.17 kg Total Chemical Oxygen Demand (TCOD) /m3.day with a food to microorganism ratio of 2.86 g TCOD/g Volatile Suspended Solids (VSS).day. These removal efficacies were attained for a hydraulic retention time of 18 hours for both SBRs with a solids retention time of 5 days for SBR-1 and 7 days for SBR-2. Both reactors were operated at a mesophilic temperature range of 23 to 26˚C and a pH range of 5 to 8.5. The temperature was left unadjusted because it was observed that it did not hinder any microbial activities during the biodegradation process. The Michealis-Menten’s and Monod models were implemented to study the substrate utilisation rate kinetics and microbial growth rate kinetics recording 15 141 g COD/m3.day; 12 518 g VSS/g VSS.day; 20 343 g COD/m3.day and 16 860 g VSS/g VSS.day for SBR-1 and SBR-2, respectively. The Monod model demonstrated a strong correlation fit between the substrate utilisation rate and microbial growth rate recording a polynomial correlation constant of R2 = 0.947 and 0.9582 for SBR-1 and SBR-2, respectively. The findings of this study showed that the cyclic aerobic-anaerobic configuration on a laboratory scale SBR inoculated with activated sludge for treatment of brewery wastewater for biological nutrients was feasible.
The biosorption of chromium and copper from AMD contaminated water using banana peels as a biomass adsorbent
(2022-09-29) Mzimela, S'thembile; Musonge, Paul; Bakare, Babatunde F.
The presence of heavy metals in water from industrial activities negatively affects human health. Metal accumulation in human bodies is toxic and can lead to carcinogenic effects when consumed for prolonged periods. There is no acceptable method for permanently removing heavy metals in water. As a result, water for human consumption and domestic use from various water sites contains harmful heavy metals. This study investigates the removal of hexavalent chromium (Cr6+) and copper (Cu 2+) from drinking water through the adsorption process using banana peels as biomass material. Banana peels were evaluated for their ability to remove heavy metals from water as a cheaper alternative resource to conventional adsorbents such as activated carbon. Cr6+ and Cu2+ are some of the most common heavy metals found in potable (drinking) water and they were chosen for this study amongst other heavy metals. Batch studies were conducted using water that was synthesized with the chosen metals. Parameters such as pH, agitation speed, biosorbent dose, initial metal concentration, and contact time were varied to determine their effect on biosorption. pH was varied between 2 and 7, agitation speed was varied between 100 and 200 rpm, dosage was varied between 1 and 6 grams, initial concentration was between 5 and 100 mg/L and contact time was also varied between 5 and 140 minutes. Each variable was done one factor at a time while keeping other values constant. The height of the column for column studies was studied between 5 and 30 cm at constant pH “4”, 5mg/L initial metal concentration and volumetric flowrate of 4mL/min. Results from the study showed that pH for both Cr6+ and Cu2+ was highest at pH “4” with % removal of 65% and 94%, respectively. Agitation speed had a high % removal at 180 rpm for Cr6+ (67%) and 160 and 180 rpm for Cu2+ (95%). Increase in biosorbent dose also increased biosorption efficiency from 17% to 95% for Cu2+ across the range, and from 58% to 65% for removing Cr6+ . In the study of initial metal concentration, banana peels performed better at lower metal concentrations for both metals. Highest % removal efficiency for Cr6+ was found at 5 mg/L at 64% and for Cu2+ at 10, 15 and 20 mg/L at 95%. Contact time between 5 and 140 minutes found that equilibrium was reached within 30 minutes for Cr6+ and within 50 minutes for Cu2+ . Adsorption equilibrium isotherms and kinetics were studied for both metals and found that the biosorption of Cr6+ followed the Freundlich isotherm and Langmuir isotherm models with R 2 of 0.99 and 0.95 respectively, and the process kinetics followed the pseudo-second-order kinetic reaction with R 2 of ~ 1. The biosorption of Cu2+ followed the Langmuir isotherm model with R 2 of 0.96 and Langmuir qm of 15.41 mg/g and the process kinetics followed the pseudo-first-order kinetic reaction as well as the intra-particle diffusion model with both R 2 of 0.98. Banana peels were characterized for their properties and the Fourier transform infrared (FTIR) spectroscopy identified the functional groups in the peels which were hydroxyls, carboxylic acids, alkanes, and amines. Most of the groups were active in the removal of Cr6+ and Cu2+. The scanning electron microscopy (SEM) identified the surface of the peels to be rough with uneven areas and the energy-dispersive x-ray spectroscopy (EDS) analysis identified the elements present in the peels which were carbon (C), oxygen (O), potassium (K), chloride (Cl) and silicon (Si). The x-ray diffraction (XRD) was used to identify the phase of the peels and it was found that the peels were amorphous with some crystallinity containing a crystal salt called sylvite. The Brunauer–Emmett–Teller (BET) analysis identified the pores of the banana peels to be mesoporous with a pore size of 2.9 nm, a surface area of 5.69 m2 /g, and a pore volume of 0.002605 cm3 /g. Column experiments in a fixed-bed column were studied for the removal of Cr6+ and the breakthrough time tb increased from 10 min at 5cm to 420 min at 30 cm. The mass transfer zone HB also increased from 0.206 at 5 cm to 7.426 at 30 cm. Other column performance indicators such as the adsorbent exhaustion rate (AER) and the number of volumes processed (NBV) showed that biosorption was efficient and dependent on bed height for better performance. The process favoured the Adams-Bohart model with R2 ranging between 0.94 to 0.98 and the Yoon-Nelson model with R2 ranging between 0.93 and 0.97. It can be concluded from this study that banana peels have the ability of removing Cu and Cr in potable water and has provided some insight for scaling-up of adsorption columns.
Chemical oxygen demand (COD) fractionation for process modelling considerations and optimization
(2021-03) Jwara, Thandeka Yvonne Sthembile; Musonge, Paul; Bakare, Babatunde F.
Wastewater treatment is a critical chain in the urban water cycle. Wastewater treatment prevents the toxic contamination of water bodies. The notable consequences of contamination are the loss of aquatic life, upsurge of eutrophication due to nutrient overload, and potential loss of human life as a result of waterborne diseases. Wastewater works (WWW) are therefore an intrinsic component of protecting the urban water cycle and ensuring that water resources are preserved for future generations. The operation of a WWW is subject to compliance with the national legislative requirements imposed by the Department of Water and Sanitation (DWS) to ensure the preservation of water resources. These requirements oblige water and sanitation departments to employ innovative design, control and optimization of WWW. Wastewater modelling packages have presented the opportunity to simulate the wastewater treatment processes in order to maintain and sustain legal compliance with the DWS. The successful implementation of a simulation package for wastewater process optimization and modelling depends on an accurate characterization also known as fractionation of the organic fractions of the WWW influents. This thesis is a result of a comprehensive study reported for Darvill wastewater work. Darvill WWW is a 60 ML/D plant which has been receiving flows of up to 120 ML/D. The importance of the study was to motivate for the upgrade of the wastewater work to account for the increased hydraulic, organic and nutrient loading into the plant. The study looked at the application of the World Engine for Simulation and Training (WEST) and all studies required to generate data that will serve as input with the understanding the current state of Darvill WWW in terms of performance. The study presents the fractionation outcomes of the primary wastewater effluent organic matter as chemical oxygen demand (COD) and the performance by assessing the biological nutrient removal process (BNR) using BNR efficiencies in addition to the development of the Darvill WWW WEST model with the aid of the probabilistic fractionator. The fractionation was achieved through the oxygen uptake rate experiments using the respirometry method. Experiments yielded the following results: biodegradable COD (bCOD) (70.5%) and inert COD (iCOD) (29.5%) of the total COD. Further characterization of the bCOD and iCOD yielded the readily biodegradable fraction (SS) at 75%, slowly degradable (XS) at 25%, particulate inert (XI) was 50.8% and the inert soluble SI at 49.2%. The COD fractions were used and served as input to the development and evaluation of the Darvill WEST model. Calculations of BNR efficiencies were used to evaluate the effects of high inflow to the biological treatability of the activated sludge for the period September 2016 - November 2017. It was found that at inflows above design capacity, the nutrient removal efficiency reduced from an expected 80-90% to an average of 40% with an average soluble reactive phosphorus (SRP) removal efficiency being 64%. A data input file for the period of January – June 2016 was created to serve as input into WEST to develop a baseline average model for the Darvill WWW plant. The model results predicted a mixed liquor suspended solids (MLSS) concentration of 6475 mg/L for the plant during the study period this was comparable with the plant MLSS concentration of 6700 mg/L at the time which was above the design concentration of 4500 mg/L. This was largely due to the plant operating under nutrient overload conditions. The final effluent (FE) concentration in the defractionation model was found to be COD = 41.28 mg/L, ammonia (NH3) = 22.02 mg/L, Total Suspended Solids (TSS) = 32 mg/L, SRP = 2.16 mg/L. Most of these results were expectedly non-compliant to the discharge limits imposed by the DWS with the exception of COD. The plant FE measurements were COD = 45.1 mg/L, NH3 = 3.4 mg/L, TSS = 20.9 mg/L, SRP= 6.67 mg/L. The COD and TSS prediction were comparable to the model prediction however there were limitations in the models ability to predict NH3 and SRP. The model does not account for changes in dissolved oxygen (DO) and temperature as these parameters are kept constant for the purpose of this study. The model assumes a temperature of 20 oC and a DO concentration of 2 mg/L for the aerobic reactor, 0.01 mg/L for the anaerobic reactor and 0.1 mg/L for the anoxic reactor. The model assumes that with the nutrient overload, oxygen compensation occurs within the reactor to maintain a constant DO concentration within the units. This limits the model in the prediction of actual instance where the overload would deplete the DO and where other competing reactions would give rise to greater non-compliances as well as biological growth’s impairment due to cold weather conditions.
Evaluation of veterinary antibiotics in a swine slaughterhouse wastewaters and their removal using advanced oxidation processes
(2020-01) Chollom, Martha Noro; Rathilal, Sudesh; Swalaha, Feroz Mahomed; Bakare, Babatunde F.
Antibiotics are found in low concentrations in water sources and surrounding environments. Despite their presence in low concentrations in the environment, they are associated with antibiotic resistant bacteria (ARBs) in water sources thus necessitating stringent legislations worldwide. The burden of ARBs has drawn worldwide attention into investigating this rising phenomena to better understand the seriousness of the effects of these contaminants. Studies conducted, however, have mostly been in the developed nations, and the focus has been on human pharmaceuticals. Information on veterinary pharmaceuticals is very limited, even though, the veterinary pharmaceuticals are known to cause as much havoc as human pharmaceuticals. Given the considerable impact that the veterinary antibiotics can have on humans and the environment, there is need for thorough investigations to be done regarding their detection and removal from water sources using biological and other appropriate technologies such as advanced oxidation methods. However, there is very little that has been done to date in this area globally and in South Africa in particular which highlights the novelty of this work. The findings of this study will therefore inform future decision making by policy makers and governments in handling these veterinary antibiotics in water sources. This study was divided into four phases covering the five objectives investigated. The first phase covered the first and second objectives, in which a suitable and sensitive analytical method was developed for the determination of veterinary antibiotics based upon solid phase extraction (SPE), ultrahigh liquid chromatography with photodiode array detectors (PDA) and mass spectrometry (MS) (UHPLC-PDA-MS). Four classes of antibiotics were selected: tetracycline, β-lactam, sulphonamides and fluoroquinolones. The studied antibiotics were extracted from slaughterhouse wastewater samples using strata-X cartridges. The extraction of antibiotics from water matrices was tested at several pH values. The best recoveries were obtained at pH 2. Depending on the nature of antibiotic, the limits of detection (LOD) and limits of quantification (LOQ) were in the range of 0.1–0.3 μg/L and 1.3–2.9 μg/L, respectively. The range of antibiotics detected in the wastewaters in effluents was 0.008 to 4.9 ng/L while in the influent, the range was 1 to 21 ng/L; thus higher concentrations were found in the influents as compared to effluents. This therefore confirmed the presence of these contaminants in the South African slaughterhouse wastewaters. The second phase entailed the investigation of the third objective which was to determine the possible mechanisms of removal of antibiotics from wastewaters using anaerobic digestion and to evaluate the biodegradation kinetics. A laboratory scale upflow anaerobic sludge blanket (UASB) reactor was employed to treat synthetic wastewater to explore the removal efficiencies of five veterinary antibiotics with an initial concentration of 50 µg/L. In a like manner, batch reactors were further used to evaluate the removal routes of the antibiotics. The UASB reactor was operated continuously under mesophilic conditions to evaluate its performance regarding the removal of organics; biogas production was also monitored. Organic loading rate (OLR) was varied from 8 to 9.2 kg.COD.m-3.d-1while keeping the hydraulic retention time (HRT) constant at 12 h. A chemical oxygen demand (COD) removal efficiency higher than 75% was achieved at an OLR of 9 kg.COD.m-3.d-1, with a HRT of 12 hours. About 80% of the antibiotics were removed during the continuous processes, however, a distinctive pattern of removal was not observed. The kinetic studies using a batch process showed that the removal route for the antibiotics was majorly adsorption to the sludge. Biodegradation occurred alongside adsorption but to a lesser degree. The kinetic data showed that the antibiotics degradation followed a first order kinetic model with half-lives that ranged from 6 to 77 days. Given the ineffectiveness of the biological process against the antibiotics, there was need to explore alternative wastewater treatment technologies. In this case adsorption and photocatalysis were investigated. Phase three presents the preparation and characterization of the integrated photocatalyst (IPCA). The adsorption properties of the IPCA, titanium dioxide (TiO2) and activated carbon (AC) were assessed using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). These adsorbents were used to treat wastewater containing the target antibiotics. The effect of process variables such as adsorbent concentration, contaminant concentration and solution pH was investigated. The IPCA demonstrated good adsorption ability attaining removal efficiencies of over 50% while AC efficiency was over 60%. However, TiO2 demonstrated negligible adsorption performance. In the fourth phase, objective five was evaluated to determine the effectiveness of advanced oxidation processes (in this case photocatalysis) using IPCA and TiO2. The effect of process variables such as photocatalyst concentration and solution pH were investigated. It was found that photocatalysis attained almost 100% degradation of the target contaminants. Maximum removal efficiencies for both AC and IPCA were above 50% for an initial concentration of 100 mg/L. Adsorption using AC and IPCA followed the Langmuir and Freundlich isotherms, however, higher coefficients of correlation were obtained for the Langmuir isotherms for four of the antibiotics viz. AMO, CIP, ENRO and TET. The Freundlich model was the best fit for the SULFA in terms of the coefficient of correlation. With regards to the photodegradation, it was found that photocatalysis attained almost 100% degradation of the target contaminants. Complete degradation was achieved within half-lives of 60 to 102 minutes for all the compounds. Although both photocatalysts effectively degraded the contaminants, the IPCA had the unique advantages of possessing both adsorptive and photocatalytic properties. The activated carbon in the IPCA provided sites for the attachment of the antibiotics and TiO2 thus enhancing the photocatalytic performance. Apart from this, the IPCA can be easily recovered for reuse by decantation unlike the slurry TiO2. Therefore, the study demonstrated the effectiveness of the IPCA as a suitable photocatalytic material for the complete degradation of these antibiotics.
Modelling and optimization of competitive bio-sorption of copper and lead ions using fruit peels
(2022-09-29) Afolabi, Felicia Omolara; Musonge, Paul; Bakare, Babatunde F.
The application of various agricultural-based materials as adsorbents for the removal of heavy metal ions from aqueous solutions has attracted the interest of many researchers. Many studies have been conducted on the removal of heavy metals from wastewater using the bio-sorption process with a focus on wastewater containing single solutes. In addition, the existing column adsorption models were developed to describe the dynamic behaviour of single solute biosorption processes. However, the application of a linear driving force model which makes use of batch experimental results to describe the bio-sorption process in a fixed-bed has not been reported for binary solute systems. In this study, the performance of orange and banana peels was investigated for the removal of copper and lead ions from wastewater in both single and binary systems. These bio-sorbents were used in their natural form. The characterization of the bio-sorbents before and after adsorption was achieved using analytical techniques. Fourier Transform Infrared Spectroscopy (FTIR) was used to determine the functional groups present on the surface of the bio-sorbents. The results showed that the bio-sorbents contain various functional groups such as carboxyl, hydroxyl, carbonyl, aminyl, and alkyl groups that enhanced the adsorption process. After adsorption, there were significant shifts in the peaks representing hydroxyl and carboxyl groups which were common to both biosorbents. Therefore, it was concluded that ion exchange is the sorption mechanism responsible for the adsorption of metal ions. The Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM/EDS) was used to determine the morphological structure and the elemental composition of the bio-sorbents. The surfaces of the bio-sorbents showed an irregular, and microporous structure while the elemental composition revealed the presence of carbon, oxygen, hydrogen, and potassium. The surfaces of the bio-sorbents became uniform, smooth, and covered after the adsorption and the EDS showed the presence of adsorbed metal ions. The X-ray diffractometer (XRD) which explained the crystallinity of the bio-sorbents showed that both bio-sorbents are amorphous. The values of the point of zero charge (pHpzc) for orange and banana peels obtained were 3.85 and 4.83 respectively. This revealed that the surfaces of both bio-sorbents were acidic and therefore suitable for the adsorption of cations. The design of experiments (DOE) was employed in the batch study to investigate the interactive effect of the operating parameters, and a 24 full factorial design was used to generate the experimental runs. The factors studied and their ranges are initial concentration (10 – 100 mg/L), solution pH (2 - 6), adsorbent dosage (0.1 – 1 g), and particle size (75 – 455 µm), for the single solute system. The interaction of the factors was studied using response surface methodology (RSM) with the central composite design (CCD). The highest removal of lead and copper for orange peels was 99.75% and 98.53% while 99.32% and 98.12% were obtained for lead and copper using banana peels. The results showed that both bio-sorbents have a high affinity for lead and copper while the order of influence of the factors gave adsorbent dosage > pH > initial concentration > particle size for the bio-sorption of copper and lead using both bio-sorbents. The optimum pH of 5.5 was obtained for both metals hence three factors (initial concentration, adsorbent dosage, and particle size) with the same parameter range specified for a single solute were considered for the binary solute interactive study using the same method. The initial concentration of the metal ions in the binary system was in the ratio of 1:1. In most of the experimental runs, the percentage yield of lead was higher than copper. The highest removal for lead and copper was 98.85 % and 87.32 % for orange peels, while for banana peels, lead was 97.85 % and copper was 97.6 %. The isotherm and kinetic studies of single and binary systems of copper and lead were carried out using both bio-sorbents. The Langmuir isotherm fitted the adsorption data signifying a monolayer adsorption mechanism while the pseudo-second-order model fitted the kinetic data which suggested the chemisorption process for both bio-sorbents in single and binary systems. The adsorption of lead was higher than copper in both single and binary systems and the adsorption of copper was sensitive to the co-existence of lead in binary systems. Orange peels bio-sorbent performed slightly better than banana peels hence, it was chosen for the dynamic column studies The fixed bed experiments were conducted to investigate the effect of column parameters such as flow rate (1 and 3 mL/min), initial concentration (10, 50, and 100 mg/L), and bed height (1 and 3 cm). The results showed that the performance of the bed was improved with an increase in the bed height while the volume of solution treated at breakthrough decreased with an increase in flow rate for both metals in a single solute system. The Thomas, Yoon Nelson, and Bohart Adams models were applied to the experimental data. The Thomas and Yoon Nelson models performed well with a high coefficient of correlation (R2 > 0.9) and the lowest mean absolute error value of less than 0.1. The breakthrough curves for the binary solution of copper and lead showed slightly different shapes than the single solute system. This can be ascribed to the influence of the co-existence of metal ions which led to competition for the limited binding sites on the bio-sorbent. The breakthrough time decreased with an increased initial concentration for both metal ions in the binary system. However, the breakthrough curves representing copper bio-sorption, reached the breakthrough point faster than lead suggesting a lower affinity of copper to bind to the active site. The bio-sorption capacity of lead was consistently higher than copper for all the initial concentrations considered. A mathematical model was developed for the binary solute system of copper and lead. The model was developed from the mass balance equation of the solid and liquid phases of an elemental section of the column. An assumption of axially dispersed plug flow was made, and a linear driving force (LDF) was used to describe the intraparticle mass transfer. The partial differential equation obtained from the mass conservation equation was discretized to form an ordinary differential equation (ODE) using the finite difference method. The resulting ODEs were solved using the ode15s solver in MATLAB. The mathematical model results followed a similar trend with the experimental results, such that the breakthrough curve of copper reached the breakthrough point faster than lead for all the initial concentrations considered. The model results showed that the mathematical model based on the linear driving force can be used to describe the dynamic behaviour of a bi-solute fixed-bed adsorption column. The mathematical model performed well at high initial concentrations. The Thomas model gave the lowest mean absolute error (MAE) value of 0.08 while the mathematical model gave an MAE value of 0.9 which explains the deviation of the models from the experimental results. In conclusion, the equilibrium isotherm studies carried out in the batch experiments were used to assess the adsorption capacity of the bio-sorbent which was used in the LDF expression of the model. Hence, this study has demonstrated that the mathematical model developed for the binary system is suitable for predicting the breakthrough curves using batch experimental results
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.
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.