Wastewater Treatment by Physical, Chemical, Photochemical, and Biological Processes, and Their Combinations

The anaerobic baffled reactor (ABR) is a decentralized treatment system that is commonly used for municipal wastewater treatment. Slower growth rate of anaerobic microorganisms requires extended hydraulic retention time (HRT), leading to a larger bioreactor volume. In this study, polyurethane sponge sheets were provided in a six-compartment ABR for retention and growth of biomass to improve its treatment performance at shorter HRTs. Polyurethane sponge was selected for its low cost, durability, availability, easy emplacement, and high voidage. The sponge anaerobic baffled reactor (SABR) was operated within a temperature range of 35 ± 1 °C at HRTs of 18, 12, 8, and 6 h to evaluate its treatment performance. Average removal efficiencies ranged from 60–77% for organics, 74–81% for total suspended solids (TSS), 50–66% for total nitrogen (TN), and 47–57% for total phosphorus (TP). The shortest HRT was 8 h with average removal efficiencies of 74, 63, 64, and 52% for organics, TSS, TN, and TP, respectively, to meet effluent discharge limits. With the shortest HRT of 8 h, the SABR demonstrated low volume requirements, thereby making it an efficient solution for decentralized wastewater treatment, particularly advantageous for developing countries with warm climates. Full article

The application of fixed activated sludge with an attached growth process (FASAG) with optimal operating conditions (hydraulic retention time (HRT) of 7 h, dissolved oxygen (DO) of 6 mg/L, and alkalinity dosage of 7.14 mgCaCO₃/mgN-NH₄⁺) treats wastewater generated from office buildings to meet discharge requirements (as per the regulation in the nation where the study was conducted) with typical parameters such as pH of 6.87–7.56, chemical oxygen demand (COD) of 32–64 mg/L, suspended solids (SS) of 8–11 mg/L, N-NH₄⁺ of 1–7 mg/L, and denitrification efficiency reaches 53%. In addition, the FASAG is an outstanding integration that makes both economic and environmental sense when applied in local wastewater treatment systems. In particular, this process combines aerobic and anoxic processes in a creation tank. This explains why this approach can save investment and operating costs, energy, and land funds. In office building regions, where land area is frequently limited, saving land funds presents numerous options to enhance the density of green cover. Furthermore, as a new aspect, investing in reusing wastewater after treatment to irrigate plants or flush toilets in office buildings contributes to a decrease in the quantity of wastewater released into the environment, saving water resources and supporting sustainable development. Full article

Implementing efficient and cost-effective wastewater treatment methods in wastewater treatment plants (WWTPs) is crucial for ensuring sustainable development in contemporary societies. This study explores the feasibility of a continuous UV/${\mathrm{H}}_2{\mathrm{O}}_2$ tubular photoreactor as a pre-treatment to enhance the biodegradability of aqueous polyvinyl alcohol (PVA) solutions, known as a nonbiodegradable wastewater. Using a combination of a Box–Behnken design (BBD) and the response surface methodology (RSM), three main process variables, including the PVA feed concentration, the inlet ${\mathrm{H}}_2{\mathrm{O}}_2$ concentration, and the PVA feed flow rate, are studied within ranges of 500–1500 mg/L, 390–780 mg/L, and 50–150 mL/min, respectively. The results show significant interaction effects between the PVA feed and inlet ${\mathrm{H}}_2{\mathrm{O}}_2$ concentrations on the effluent ${\mathrm{B}\mathrm{O}\mathrm{D}}_5$/COD ratio. The optimal operating conditions are determined using the RSM, with a PVA feed concentration of 665 mg/L, an inlet ${\mathrm{H}}_2{\mathrm{O}}_2$ concentration of 390 mg/L, and a PVA feed flow rate of 59 mL/min. Operating at this point leads to an increase in the effluent ${\mathrm{B}\mathrm{O}\mathrm{D}}_5$/COD ratio from 0.15 to 0.53, which is validated experimentally with a ±5% error. Under these conditions, the effluent demonstrates an enhanced biodegradability, allowing for redirection to a subsequent biological post-treatment phase. This study demonstrates that using the UV/${\mathrm{H}}_2{\mathrm{O}}_2$ process to enhance the biodegradability of an aqueous PVA solution is more economical than focusing on the complete removal of total organic carbon (TOC). Also, a comparison of these results with those of our previous study indicates that wastewater becomes more biodegradable by progressing the UV/${\mathrm{H}}_2{\mathrm{O}}_2$ process due to the breakdown of polymer molecules, which reduces their molecular weight and makes them more consumable for biomass. Full article

The treatment of pharmaceutical wastewater is a critical environmental challenge, necessitating efficient removal methods. This study investigates the adsorption of a synthetic multicomponent pharmaceutical wastewater (SPWW) containing methanol, benzene, methylene chloride, 4-aminophenol, aniline, and sulfanilic acid onto charcoal-based activated carbon (AC). Batch experiments were conducted to study the effects of pH, contact time, and initial concentrations of the adsorbates. The results show that longer contact time and higher initial concentrations increase the adsorption capacity, whereas pH shows no significant effect on the adsorption capacity at a value of less than 10, eliminating the need for pH adjustment and reducing process costs. The pseudo-second order (PSO) kinetic model best describes the adsorption process, with intraparticle diffusion playing a key role, as confirmed by the Weber and Morris (W-M) model. Six models describing the adsorption at equilibrium are applied to experimental data, and their parameters are estimated with a nonlinear regression model. Among isotherm models, the Langmuir-Freundlich model provides the best fit, suggesting multilayer adsorption on a heterogeneous granular activated carbon (GAC) surface. The maximum adsorption capacity is estimated to be 522.3 mgC/gAC. Experimental results confirm that GAC could effectively treat highly concentrated pharmaceutical wastewater, achieving up to 52% removal efficiency. Full article

This study aims to evaluate the emissions of greenhouse gases (GHGs) stemming from the sludge treatment sector in China and to investigate the feasibility of novel technologies in curtailing these emissions, with the aim of fostering sustainable sludge management methodologies. Employing a life-cycle assessment (LCA) methodology, the research computed the comprehensive GHG emissions resulting from sludge treatment, taking into consideration diverse elements such as treatment techniques (e.g., landfills, incineration, and land application) and the geographical variations among China’s 660 municipalities. Findings indicate that the total amount of GHG emissions from sludge treatment amounted to 18.54 Mt CO₂-eq in 2017, with incineration registering the highest emissions (10,011.53 kg CO₂-eq/t dry sludge (DS)), followed by landfills (717.51 kg CO₂-eq/t DS) and land application (276.41 kg CO₂-eq/t DS). The geographical dispersion of emissions characteristics reveal notable regional disparities, with the top 1% of cities responsible for 34.2% of the overall emissions. The concentration of emissions in the top 1 percent of cities underscores the necessity for tailored mitigation measures that consider localized sustainable development challenges. Principal component analysis (PCA) demonstrates that economic determinants and treatment scales exert substantial influence on emissions, underscoring the imperative of aligning Sustainable Development Goals (SDGs) with economic advancement. To curtail the carbon footprint associated with sludge treatment and enhance sustainability, the study evaluated the emission mitigation potential and expenses of diverse technologies, encompassing thermal conversion, anaerobic digestion, hydrothermal treatment, and wet oxidation. These technologies have the capacity to slash GHG emissions by 0.09–0.46 t CO₂-eq/t DS in comparison to traditional approaches, while concurrently advancing resource recuperation and principles of circular economy. For instance, gasification could diminish GHG emissions by 0.33–0.46 t CO₂-eq/t DS, whereas anaerobic digestion could yield reductions of 0.09–0.30 t CO₂-eq/t DS. The implementation of these innovative technologies across 660 Chinese municipalities could potentially curtail total GHG emissions from sludge treatment by 15–40%. Nevertheless, further enhancements are imperative to refine their environmental and economic efficiency and guarantee enduring sustainability. By deploying these technologies and embracing optimization tactics, China’s sludge treatment sector can make a substantial contribution towards attaining national carbon neutrality objectives and advancing sustainable development. Full article

During the COVID-19 pandemic, polypropylene waste generated in hospitals increased significantly. However, conventional strategies for the final disposal of environmental waste, such as incineration, proved inefficient due to the generation of toxic chemical species. In this research, these PP wastes were mixed with 1.5, 20, 150, 200, and 400 mg of iron oxide (FeO), extruded, and pelletized to obtain samples HW-PP-0, HW-PP-1, HW-PP-2, HW-PP-3, and HW-PP-4, respectively. XRF, TGA, and GC-MS characterized these samples. The samples were subjected to pyrolysis and thermo-oxidative degradation with controlled currents of nitrogen and oxygen. The characterization of the gases resulting from pyrolysis was carried out with a GC-MS, where the results showed that HW-PP-0 (mixed with 1.5 mg of FeO) presented the highest concentrations of alkanes (35.65%) and alkenes (63.7%), and the lowest levels of alkynes (0.3%), alcohols (0.12%), ketones (0.04%), and carboxylic acids (0.2%). The opposite was observed with the hospital waste HW-PP-4 (mixed with 400 mg of FeO), which presented the highest levels of alkynes (2.93%), alcohols (28.1%), ketones (9.8%), and carboxylic acids (8%). The effect of FeO on HW-PP-O during thermo-oxidative degradation generated values of alkanes (11%) and alkenes (30%) lower than those during pyrolysis. The results showed the catalytic power of FeO and its linear relationship with concentration. This research proposes the mechanisms that can explain the formation of different functional groups of various molecular weights which allow us to understand the presence of alkanes, alkenes, alkynes, alcohols, ketones, and carboxylic acids. Full article

The recovery concept of cleaning solutions, based on single-phase detergents from cleaning-in-place (CIP) effluents from the dairy industry, is presented. The first step consists of ultrafiltration (UF) (with a cut-off of 5 or 10 kDa) to reduce the high load of milk proteins, followed by nanofiltration (NF) (with a cut-off of 200 Da) to separate low molecular weight lactose. Membrane steps were performed in the concentration mode, achieving a recovery of 75% of the solutions. UF modules reduced 70–85% of chemical oxygen demand (COD), 99% of milk proteins, and 45–70% of lactose, limiting the susceptibility of NF modules to fouling. Combined with nanofiltration, the efficiency of the purification system is 100% for proteins and more than 99% for lactose. The solutions recovered in the proposed purification variants are recognized as sodium hydroxide solutions with a surfactant admixture, and they can be successfully re-used for cleaning processes in the production plant. Full article

Treating high-strength fresh leachate is challenging and of great interest due to the inherent variability in its physical and chemical characteristics. This research aims to enhance the efficiency of the anaerobic hybrid reactor (AHR) series in treating high-strength fresh leachate and achieving biogas generation from fresh leachate at ambient temperatures. The AHR series used consists of two serially connected reactors termed the first anaerobic hybrid reactor (AHR-1) and the secondary anaerobic hybrid reactor (AHR-2). AHR-1 treated high-concentration fresh leachate with an organic loading rate (OLR) between 5 and 20 kgCOD/m³·d. AHR-2 treated the effluent from the first tank and removed organic matter from the system. The experiment was conducted for 210 days, showing that an OLR of 10 kgCOD/m³·d resulted in the most suitable COD removal efficiency, ranging from 82 to 91%. The most suitable OLR for biogas production was 15 kgCOD/m³·d. The AHR series proved to be an efficient system for treating high-strength fresh leachate and generating biogas, making it applicable to leachate treatment facilities at waste transfer stations and landfill sites. Treating leachate and utilizing it as a renewable energy source using the AHR series presents a practical and efficient waste management approach. High-strength leachate can be effectively treated with the AHR series; such methods may be integrated into industries treating leachates with high COD values. Full article

This review emphasizes the significance of formulating control strategies for biological and advanced oxidation process (AOP)-based wastewater treatment systems. The aim is to guarantee that the effluent quality continuously aligns with environmental regulations while operating costs are minimized. It highlights the significance of understanding the dynamic behaviour of the process in developing effective control schemes. The most common process control strategies in wastewater treatment plants (WWTPs) are explained and listed. It is emphasized that the proper control scheme should be selected based on the process dynamic behaviour and control goal. This study further discusses the challenges associated with the control of wastewater treatment processes, including inadequacies in developed models, the limitations of most control strategies to the simulation stage, the imperative requirement for real-time data, and the financial and technical intricacies associated with implementing advanced controller hardware. It is discussed that the necessity of the availability of real-time data to achieve reliable control can be achieved by implementing proper, accurate hardware sensors in suitable locations of the process or by developing and implementing soft sensors. This study recommends further investigation on available actuators and the criteria for choosing the most appropriate one to achieve robust and reliable control in WWTPs, especially for biological and AOP-based treatment approaches. Full article

The quality of simulations for wastewater treatment plants is heavily dependent on the quality of the simulation input data. Inflow data from wastewater treatment plants collected by measurement cannot usually be used directly for a wastewater treatment plant simulation. A method is presented with which dynamic inflow descriptions for simulation studies can be generated from typical operational measurements. These are volume-proportional 24 h composite samples and continuously recorded inflow water flow rates. To derive the method, a deterministic model was first developed to describe typical dry weather daily inflow concentration patterns and validated for a larger number of measured daily inflow measurements (2 h composite samples). In the second part of the article, the method is then developed with which the dynamic wastewater treatment plant inflow can be calculated for a longer period of time from the modelled dry weather daily inflow and a high-resolution time series of measured flow rates. This dynamic inflow can be used to validate wastewater treatment plant models if additional online measurements for effluent concentrations (e.g., NH₄-N and NO₃-N) are available. The proposed method is highly suitable for calculating an online estimate of the influent concentrations, which can be used as input information for digital twins, such as observer models and predictive controllers, based solely on the online measurement of the influent flow rate. Full article

The global concern regarding the release of micropollutants (MPs) into the environment has grown significantly. Considerable amounts of persistent micropollutants are present in industrial discharges. Depending solely on a singular treatment approach is inadequate for the effective removal of MPs from wastewater due to their complex composition. The performance of different treatment methods to meet the discharge standards has been widely studied. These efforts are classified as hybrid and sequential processes. Despite their adequate performance, the optimization and industrial application of these methods could be challenging and costly. This review focuses on integrated (sequential) and hybrid processes for MP removal from actual wastewater. Furthermore, to provide a thorough grasp of the treatment approaches, the operational conditions, the source of wastewater containing MPs, and its characteristics are detailed. It is concluded that the optimal sequence to achieve the removal of MPs involves biological treatment followed by an advanced oxidation process (AOP) with a final passage through an activated carbon column. To refine this process further, a membrane unit could be added based on the desired effluent quality. Nevertheless, considering practical feasibility, this study identifies specific areas requiring additional research to implement this integrated treatment strategy effectively. Full article

Industries are required to utilize treatment technologies to reduce contaminants in wastewater prior to discharge and to valorize by-products to increase sustainability and competitiveness. Most acid leaching gypsum purification studies have obviated the treatment of the highly acidic wastewater produced. In this work, acidic wastewater from acid leaching purification of post-consumer gypsum was treated to recover a valuable solid product and reusable water. The main aims of this work were to determine the impact of recirculating acidic and treated wastewaters on the efficiency of the acid leaching purification process and to valorize the impurities in the wastewater. Samples were characterized through X-ray fluorescence and X-ray diffraction. SimaPro 9.5 and the ReCiPe 2016 midpoint method were used for the life cycle assessment of three sustainable wastewater management approaches. The reuse of the acidic wastewater did not improve the chemical purity of gypsum. Soluble impurities were precipitated at pH 10.5 as a magnesium-rich gypsum that could be commercialized as fertilizer or soil ameliorant. The alkaline-treated water was reused for six acid leaching purification cycles without impacting the efficiency of the purification process. An acid leaching–neutralization–filtration–precipitation approach demonstrated superior overall environmental performance. Barriers and enabling measures for the implementation of an in-house wastewater treatment were identified. Full article

This study aimed to investigate the influencing factors and characteristics of granule morphology through approximately 500 d of long-term monitoring of two types of anaerobic–aerobic phosphorus-accumulating organism (PAO) and anaerobic–anoxic denitrifying PAO (DPAO) sequencing batch reactors (SBRs). The results show that granules were present in the DPAO SBR and PAO SBR after 200 d and 250 d of operation, respectively. The average diameters of the granules were 2.2 ± 0.7 mm in the DPAO SBR and 0.4 ± 0.3 mm in the PAO SBR, respectively. The DPAO granular sludge contained rod-shaped microorganisms, whereas the PAO granular sludge contained cocci-type microorganisms. A precipitated core consisting of hydroxyapatite was found in the DPAO granules. A comparative analysis conducted under various operating conditions revealed that the availability and type of the electron acceptors (EAs) may have a significant impact on granulation. This observation suggests that the presence and diversity of EAs are crucial factors for the development of different granule sizes and morphologies. Full article

This work aimed to predict the physical–chemical characteristics of leachate according to the analysis of the solubilized extract from urban household solid waste (UHSW), on a laboratory scale, in the city of Belém/PA, Brazil. The neighborhoods where the waste was collected were sectorized based on geographic and socioeconomic data, with family income as the main parameter. After collection, the material was sent to the segregation area, where a gravimetric analysis of the UHSW was performed and fractions (paper, cardboard, Tetra Pak, rigid plastic, malleable plastic, metals, glass, organic matter, sanitary waste, fabrics and rejects) were segregated. After the gravimetric characterization, it was found that the highest average proportions were 55.57% organic matter, 14.26% sanitary waste and 9.97% malleable plastic. The organic fraction was selected and subjected to drying, crushing, sieving and packaging pretreatment, and then the solubilized extract of this fraction was obtained according to NBR No. 10.006/2004 of the Brazilian Association of Technical Standards. In the analyses of the solubilized extract, values for total nitrogen (201.80 to 359.90 mg·L⁻¹), ammonia nitrogen (161 to 289 mg·L⁻¹), nitrate (10 to 40 mg·L⁻¹) and chemical oxygen demand were obtained (28,701 mg·L⁻¹ to 38,608 mg·L⁻¹), indicating the similarity of the waste solubilization conditions to those of leachate from landfills, in addition to being in noncompliance with environmental and health legislation, thus making it necessary to have an efficient waste management system, which avoids the release of waste into the environment that would result in environmental impacts similar to those of leachate contact with the environment. Full article

Wastewater discharge into aquatic systems has become a severe threat to the ecosystem. Herein, Direct Red 28 (DR28) dye removal from an aqueous solution was executed with the application of date fruit seed biochar (DFSB). Fourier transform infrared spectra (FTIR) and scanning electron microscopy (SEM) were utilized for the identification of functional groups and characteristics of the DFSB surface. A series of batch investigations were conducted to analyze pH, contact duration, biochar amount, dye concentration, temperature, and agitation speed on DR28 dye elimination from an aqueous medium by DFSB. The highest dye elimination, 97%, was recorded at a pH of 3 by DFSB at 250 mg/L DR28 dye concentration. The equilibrium data indicated the best fit with the Langmuir isotherm with R² = 0.99, showing 5.83 mg/g monolayer DR28 uptake potential. The best correlation coefficient of the sorption procedure was observed with a pseudo-second-order kinetic study. Investigations on thermodynamic variables disclosed favorable, impetuous exothermic processes. The sorption process was spontaneous as well as exothermic, which was reflected by analyses of thermodynamic parameters. DFSB showed a 33% DR28 dye adsorption ability for up to five successive cycles. DFSB-treated DR28 dye solution increased seedling growth and biochemical components of pigeon pea. The results of the present investigation revealed the significant capacity of DFSB for DR28 dye elimination. Date fruit seed biochar can be applied as an environmentally benign, sustainable adsorbent for DR28 dye removal from industrial effluent, as it is available at zero cost and converts wastewater into reusable biomaterial. Thus, the application of DFSB can assist in wastewater treatment, carbon sequestration, and waste management for a sustainable future. Full article