Applicability of advanced oxidation processes for the reuse of laundry wastewater

Wastewater treatment is a global concern, especially in developing countries with limited access to safe and clean facilities, resulting in individuals practicing unsafe and unsustainable human practices. This poses challenges for South African wastewater treatment plants (WWTPs) due to the aging infrastructures and the use of conventional technologies. Also, recent population growth, urbanization, and industrial activities have given rise to contaminating water resources with recalcitrant organic micropollutants (OMPs). Organic micropollutants cause severe environmental pollution, imbalanced ecosystems (aquatic life), human health risks, and oxygen depletion due to accelerated chemical oxygen demand (COD). Apart from the detrimental effects of wastewater on human health and the ecosystem, the United Nations (UN) sustainability development goal of obtaining clean water and sanitation (SDG #6) by 2030 is continuously threatened. Therefore, treating wastewater for reuse in the environment with good quality comes in handy. Against this background, photocatalysis, such as the advanced oxidation process (AOP), is reported as a promising, eco-friendly, and cost-effective technology for degrading organic contaminants (COD) into harmless compounds. However, the TiO2-based photocatalytic process has setbacks, such as recoverability and treatability efficiency, limiting its industrial application. Therefore, this study explored oxide and non-oxide photocatalysts as alternatives to TiO2-based photocatalytic processes for a local South African wastewater treatment. The photocatalysts considered were Titanium dioxide (TiO2), Iron (III) oxide (Fe2O3), Zinc Sulphide (ZnS), and Copper Sulphide (CuS). Their applicability was conducted experimentally by evaluating and optimizing the performance of oxide (TiO2, Fe2O3) and non-oxide (ZnS, CuS) photocatalysts under UV, UV-visible, and natural sunlight irradiation. The One-Factor-at-a-Time (OFAT) approach was used on the photocatalytic system to identify the relationship between the variables that influence the photocatalytic degradation treatment of municipal wastewater. The water quality parameters considered were pH, turbidity (NTU), colour (Pt. Co), and COD (mg/L). By employing the oxides and non-oxides under a constant UV irradiation light source vi and OFAT approach, the catalyst load (0.5-2.5 g/L), mixing speed (30-150 rpm), and exposure time (10-60 minutes) were investigated. Among the photocatalysts, CuS displayed the best results overall for above 50% COD removal efficiency, whilst ZnS was also efficient in removing above 50% turbidity and colour at a catalyst load of 1.5 g/L, mixing speed of 90 rpm, and UV exposure time of 45 minutes. It was established that CuS was the cheapest at R2.01/1.5g as compared to TiO2 at R32.47/1.5g. Subsequently, the photocatalysts were investigated using three different light sources: UV, UV-visible, and sunlight irradiation. UV-visible was the most favourable at a catalyst load of 1.5 g/L, mixing speed of 90 rpm, and irradiation time of 60 minutes. Thus, the high light intensity of UV-visible, 191,000 Lux, enhanced the photocatalytic performance of the four photocatalysts under this study, with the optimum COD removal values at 72.25%, 70.87%, 70.20%, and 46.66% for Fe2O3, ZnS, CuS, and TiO2 respectively. Furthermore, response predictive models were developed as a function of the input factors of the photocatalytic system for the treatment of municipal wastewater. This was done utilizing the response surface methodology (RSM) via the Box Behnken design (BBD) with the best-performing catalyst (CuS) and the best light source (UV visible), at the optimal conditions of catalyst load of 2 g/L CuS, a mixing speed of 120 rpm, and an exposure time of 30 minutes with treatability desirability of 96%. The selected optimal condition was then validated experimentally, and the results obtained were agreeable with the model-predicted values at 95% confidence levels. Moreover, a comparative study with CuS and TiO2 was evaluated with synthetic wastewater (SW) and raw wastewater (RW) at the optimal conditions. The results by CuS demonstrated above 55% COD, turbidity, and colour removal from both the SW and RW compared to the TiO2, which obtained below 35% removal from both SW and RW. Therefore, under the conditions investigated in this study, CuS was found to be the most cost-effective and viable photocatalyst alternative to TiO2 for wastewater treatment. However, the techno-economic and life cycle assessment must be explored to encourage the prospects of the CuS in the water settings

COD removal from biologically stabilized landfill leachate using Advanced Oxidation Processes (AOPs)

With the increasing severity of global water pollution, traditional wastewater treatment methods have gradually revealed limitations in dealing with complex and refractory pollutants. Advanced oxidation processes (AOPs) have emerged as a promising alternative due to their ability to generate highly reactive radicals (such as hydroxyl and sulfate radicals) that can effectively degrade a wide range of pollutants. This review provides a detailed overview of various AOP technologies, including Fenton processes, ozone-based AOPs, persulfate-based AOPs, photocatalytic AOPs, electrochemical AOPs, and sonochemical AOPs, focusing on their fundamental principles, reaction mechanisms, catalyst design, and application performance in treating different types of wastewater. The research results show that the improved Fenton process can achieve a chemical oxygen demand (COD) removal rate of up to 85% when treating pharmaceutical wastewater. Photocatalytic AOP technology demonstrates higher degradation efficiency when treating industrial wastewater containing refractory pollutants. In addition to effectively degrading refractory pollutants and reducing dependence on traditional biological treatment methods, these advanced oxidation processes can also significantly reduce secondary pollution generated during the treatment process. Moreover, by optimizing AOP technologies, the deep mineralization of harmful substances in wastewater can be achieved, reducing the potential pollution risks to groundwater and soil while also lowering energy consumption during the treatment process. Additionally, this review discusses the challenges faced by AOPs in practical applications, such as high energy consumption, insufficient catalyst stability, and secondary pollution. This review summarizes the research progress and application trends of catalytically driven AOPs in the field of wastewater treatment over the past five years. It aims to provide a comprehensive reference for researchers and engineering professionals on the application of AOPs in wastewater treatment, promoting the further development and practical implementation of these technologies.

The present study was conducted in order to investigate the efficiency of different advanced oxidation processes both individually and in combination with the biological method for the removal of color and chemical oxygen demand (COD) from wastewater in the pulp and paper industry. Advanced oxidation processes include ozone, Fenton, hydrogen peroxide, and photo-Fenton. Biologically treated wastewater was successively subjected to advanced oxidation processes (AOPs). The optimum conditions for the ozone treatment of raw wastewater were found to be a contact time of 9 min and a pH of 5 at a fixed dose of ozone for a removal efficiency of 41.22% for color and 88.53% for COD. Similar optimum conditions for the ozone treatment of biologically treated wastewater showed a removal efficiency of 46.36% for color and 95.92% for COD. The photo-Fenton process also showed an efficiency comparable to the ozone treatment for both raw wastewater and biologically treated wastewater, resulting in a removal efficiency of 39.85% (color) and 90.13% (COD) for raw wastewater, and of 41.34% (color) and 94.29% (COD) for biologically treated wastewater. Each had a contact time of 12 h. The Fenton oxidation of raw wastewater showed a removal efficiency of more than 26.30% for color and 86.33% for COD. Fenton oxidation, however, showed an efficiency of 26.62% for color and 84.49% for COD removal from biologically treated wastewater. Hydrogen peroxide showed an efficiency of 28.45% for color and 85.13% for COD removal from raw wastewater, and 39.48% for color and 86.53% for COD removal from biologically treated wastewater. The results for the raw wastewater treatments indicated that higher removal efficiencies can be achieved when they are used as pre-treatments. Biological treatment is a cost-effective method but it has less efficiency for color removal. In combination with one of the AOPs, either as a pre- or post-treatment under a controlled time and dose, biological treatment increased the efficiency, making treatment feasible at larger scales.

BACKGROUND: This study considers batch treatment of saline wastewater in an upflow anaerobic packed bed reactor by salt tolerant anaerobic organisms Halanaerobium lacusrosei.RESULTS: The effects of initial chemical oxygen demand (COD) concentration (COD0 = 1880–9570 mg L−1), salt concentration ([NaCl] = 30–100 g L−1) and liquid upflow velocity (Vup = 1.0–8.5 m h−1) on COD removal from salt (NaCl)‐containing synthetic wastewater were investigated. The results indicated that initial COD concentration significantly affects the effluent COD concentration and removal efficiency. COD removal was around 87% at about COD0 = 1880 mg L−1, and efficiency decreased to 43% on increasing COD0 to 9570 mg L−1 at 20 g L−1 salt concentration. COD removal was in the range 50–60% for [NaCl] = 30–60 g L−1 at COD0 = 5200 ± .100 mg L−1. However, removal efficiency dropped to 10% when salt concentration was increased to 100 g L−1. Increasing liquid upflow velocity from Vup = 1.0 m h−1 to 8.5 m h−1 provided a substantial improvement in COD removal. COD concentration decreased from 4343 mg L−1 to 321 mg L−1 at Vup = 8.5 m h−1, resulting in over 92% COD removal at 30 g L−1 salt‐containing synthetic wastewater.CONCLUSION: The experimental results showed that anaerobic treatment of saline wastewater is possible and could result in efficient COD removal by the utilization of halophilic anaerobic bacteria. Copyright © 2008 Society of Chemical Industry

Advanced oxidation processes which produce hydroxyl radicals with high oxidation potential have come forward among the methods used in the treatment of industrial wastewaters containing organic pollutants that are difficult to biodegrade. The application of UV rays with the fentanyl reactivity showed that the organic material is more fragmented and the degradation rate is higher. In this study, Fenton process and photo-Fenton process were applied to industrial wastewater of paper. In experimental studies, optimum experimental parameters such as iron ion and hydrogen peroxide concentrations, pH, temperature, reaction time, mixing speed and light intensity were determined and processes were compared. 70% color and 51% chemical oxygen demand (COD) removal in the Fenton process; 96% color and 90% COD removal in the photo-Fenton process were obtained. The addition of UV radiation to the oxidation process resulted in better degradation of organic contaminants and enhanced color and COD removal efficiency. Although the optimum reaction time of the Fenton process was 120 minutes, the optimum reaction time of the photo-Fenton process was 60 minutes.

Application of electrochemical flow-through oxidation technology in the treatment of concentrated water from nanofiltration and reverse osmosis in the coal chemical industry

Due to the population growth and reduction of water resources, wastewater treatment and reuse vital. As the secondary wastewater treatment processes enable removes a significant amount of P and N, nutrient-rich effluents can cause eutrophication in water bodies. On the other hand, nutrients removal in sewage treatment using mechanical methods is costly and complex. The aquaculture method using Azolla filiculoides could be an appropriate option for removing total phosphorus (TP), total nitrogen (TN), and chemical oxygen demand (COD) from wastewater. Synthetic wastewater has been prepared in the typical range of municipal wastewater. Two g fresh weight of an acclimatized A.filiculoides was floated in sample bowls each one containing 500 CC prepared wastewater. Total nitrogen, TP, and COD removal by Azolla filiculoides for 21-days were optimized and investigated using the response surface methodology (RSM). For this aim, the D-optimal method was used to optimize the three independent variables (TP concentration (10.8-84.6mg l- 1), TN concentration (20-99mg l- 1), and COD concentration (66.26-415mg l- 1)) for their maximum removal efficiency of them. Experiments were performed on 28 runs in which independent variables were measured using a HACH DR 5000 spectrometer. Predicted R-squared for COD, TP, TN removal, and Azolla mass (responses) have been equal to -0.0897, 0.8514, 0.7779, and 0.5645, respectively. The model was used to maximize Azolla growth and maximize removal efficiency of nitrogen, phosphorus, and COD that occurred in minimum concentrations of TN (20mg l- 1), TP (10.8mg l- 1), and COD (66.26mg l- 1). The removal efficiency of Azolla was obtained 77.5 % for COD, 66.8 % for TP, and 78.1 % for TN in the optimum condition of independent variables. Also, increase of Azolla mass was 239 %, with desirability of 0.66. The difference between model prediction and model validation testing for Azolla mass increase, COD, TN, and TP removal was equal to ± 11.6 %, ± 7.9 %, ± 0.0 %, and ± 1.9 %, respectively. Azolla could remove phosphorus in nitrogen deficiency or even lack of nitrogen. Results indicate that removal efficiency has an upward trend as the Azolla growth increases. This kind of fern has a significant effect on removing nitrogen, phosphorus, and COD from an aqueous solution. The removal efficiency of TN, TP, and COD at optimum operating conditions showed good agreement with model-predicted removal efficiency.

Hydrogen peroxide (HP) is widely used in advanced oxidation processes (AOPs). This study evaluates the chemical oxygen demand (COD) removal efficiency of Acid Orange 8 (AO 8) at a higher concentration by modified Fenton processes using substituted HP such as tert-butyl hydroperoxide (TBHP) and sodium perborate (SPB) and sodium persulphate (SPS) as oxidants. Under optimal conditions, COD removal was found to be 72.8 and 58.9% at pH 3.0 and 6.5 in the Fenton process in 300 min.The COD removal efficiency of different systems is in the order: Fe2+/SPB>Fe2+/HP>Fe2+/TBHP>Fe2+/SPS indicating the possibility of using SPB as a substitute for HP and SPS. The order of efficiency is attributed, among other factors, to their ability to produce HO. radicals. Various anions are shown to exhibit an inhibitory effect in the order: I->Br->F->Cl->SO42->NO3-. The inhibitory effect of Cl- is observed at higher concentrations than F- and Br-, even though I- displays inhibition at all concentrations. Finally, COD removal kinetics and the degradation mechanism, based on the identified intermediate products, were determined in this study.

Removal of color, COD and determination of power consumption from landfill leachate wastewater using an electrochemical advanced oxidation processes

The aim of this study was to compare the performance of coagulation, Fenton's oxidation (Fe2+/H2O2) and ozonation for the removal of chemical oxygen demand (COD) and colour from biologically pretreated textile wastewater. FeSO4 and FeCl3 were used as coagulants at varying doses and varying colour removal efficiency was measured. For the Fenton process, COD and colour removal efficiencies were found to be 78% and 95% for the Fenton process, and to be 64% and 71% for the Fenton‐like process (Fe3+/H2O2), respectively. Ozonation experiments were conducted at different initial pH values and fixed ozone doses. Ozonation resulted in 43% COD and 97% colour removal whereas these rates increased to 54% and 99% when 5 mg/l hydrogen peroxide was added to the wastewater before ozonation at the same dose. The operating costs of all proposed treatment systems were also evaluated in this study.

Enhanced treatment of landfill leachate wastewater using sono(US)-ozone(O3)–electrocoagulation(EC) process: role of process parameters on color, COD and electrical energy consumption

Although chemical oxygen demand (COD) is an important issue for wastewater treatment, COD reduction with microalgae has been less studied compared to nitrogen or phosphorus removal. COD removal is not efficient in conventional wastewater treatment using microalgae, because the algae release organic compounds, thereby finally increasing the COD level. This study focused on enhancing COD removal and meeting the effluent standard for discharge by optimizing sludge inoculation timing, which was an important factor in forming a desirable algae/bacteria consortium for more efficient COD removal and higher biomass productivity. Activated sludge has been added to reduce COD in many studies, but its inoculation was done at the start of cultivation. However, when the sludge was added after 3 days of cultivation, at which point the COD concentration started to increase again, the algal growth and biomass productivity were higher than those of the initial sludge inoculation and control (without sludge). Algal and bacterial cell numbers measured by qPCR were also higher with sludge inoculation at 3 days later. In a semi-continuous cultivation system, a hydraulic retention time of 5 days with sludge inoculation resulted in the highest biomass productivity and N/P removal. This study achieved a further improved COD removal than the conventional microalgal wastewater treatment, by introducing bacteria in activated sludge at optimized timing.

Effects of different pretreatment methods on anaerobic mixed microflora for hydrogen production and COD reduction from palm oil mill effluent

Wastewater treatment allows for the safe disposal of municipal and industrial wastewater to protect public health and the ecosystem[...]