Integration of ozone with co-immobilized microalgae-activated sludge bacterial symbiosis for efficient on-site treatment of meat processing wastewater

Development and challenges of emerging biological technologies for algal-bacterial symbiosis systems: A review

The algal-bacterial symbiosis system (ABSS) is considered as a sustainable wastewater treatment process. This review provides a comprehensive overview of the mechanisms of ABSS for the removal of common pollutant, heavy metals, and especially for emerging pollutants. For the macroscopical level, this review not only describes in detail the reactor types, influencing factors, and the development of the algal-bacterial process, but also innovatively proposes an emerging process that combines an ABSS with other processes, which enhances the efficiency of removing difficult-to-biodegrade pollutants. Further for the microscopic level, interactions between algae and bacteria, including nutrient exchange, signaling transmission and gene transfer, have been deeply discussed the symbiotic relationship with nutrient removal and biomass production. Finally, recommendations are given for the future development of the ABSS. This review comprehensively examines ABSS principles, development, algal-bacterial interactions, and application in wastewater treatment, aiming to deepen theoretical and practical understanding and advance ABSS technology.

Resource recovery and valorization of food wastewater for sustainable development: An overview of current approaches

The food processing industry is one of the world's largest consumers of potable water. Agri-food wastewater systems consume about 70% of the world's fresh water and cause at least 80% of deforestation. Food wastewater is characterized by complex composition, a wide range of pollutants, and fluctuating water quality, which can cause huge environmental pollution problems if discharged directly. In recent years, food wastewater has attracted considerable attention as it is considered to have great prospects for resource recovery and reuse due to its rich residues of nutrients and low levels of harmful substances. This review explored and compared the sources and characteristics of different types of food wastewater and methods of wastewater treatment. Particular attention was paid to the different methods of resource recovery and reuse of food wastewater. The diversity of raw materials in the food industry leads to different compositional characteristics of wastewater, which determine the choice and efficiency of wastewater treatment methods. Physicochemical methods, and biological methods alone or in combination have been used for the efficient treatment of food wastewater. Current approaches for recycling and reuse of food wastewater include culture substrates, agricultural irrigation, and bio-organic fertilizers, recovery of high-value products such as proteins, lipids, biopolymers, and bioenergy to alleviate the energy crisis. Food wastewater is a promising substrate for resource recovery and reuse, and its valorization meets the current international policy requirements regarding food waste and environment protection, follows the development trend of the food industry, and is also conducive to energy conservation, emission reduction, and economic development. However, more innovative biotechnologies are necessary to advance the effectiveness of food wastewater treatment and the extent of resource recovery and valorization.

Biotreatment of Industrial Wastewater using Microalgae: A Tool for a Sustainable Bioeconomy

Fresh water is one of the essential sources of life, and its requirement has increased in the past years due to population growth and industrialization. Industries use huge quantities of fresh water for their processes, and generate high quantities of wastewater rich in organic matter, nitrates, and phosphates. These effluents have contaminated the freshwater sources and there is a need to recycle this wastewater in an ecologically harmless manner. Microalgae use the nutrients in the wastewater as a medium for growth and the biomass produced are rich in nutrition that can cater growing food and energy needs. The primary and secondary metabolites of microalgae are utilized as biofuel and as active ingredients in cosmetics, animal feed, therapeutics, and pharmaceutical products. In this review, we explore food processing industries like dairy, meat, aquaculture, breweries, and their wastewater for the microalgal growth. Current treatment methods are expensive and energy demanding, which indirectly leads to higher greenhouse gas emissions. Microalgae acts as a potential biotreatment tool and mitigates carbon dioxide due to their high photosynthetic efficiency. This review aims to address the need to recycle wastewater generated from such industries and potentiality to use microalgae for biotreatment. This will help to build a circular bioeconomy by using wastewater as a valuable resource to produce valuable products.

Immobilized microalgal system: An achievable idea for upgrading current microalgal wastewater treatment

Efficient wastewater treatment accompanied by sustainable "nutrients/pollutants waste-wastewater-resources/energy nexus" management is acting as a prominent and urgent global issue since severe pollution has occurred increasingly. Diverting wastes from wastewater into the value-added microalgal-biomass stream is a promising goal using biological wastewater treatment technologies. This review proposed an idea of upgrading the current microalgal wastewater treatment by using immobilized microalgal system. Firstly, a systematic analysis of microalgal immobilization technology is displayed through an in-depth discussion on why using immobilized microalgae for wastewater treatment. Subsequently, the main technical approaches employed for microalgal immobilization and pollutant removal mechanisms by immobilized microalgae are summarized. Furthermore, from high-tech technologies to promote large-scale production and application potentials in diverse wastewater and bioreactors to downstream applications lead upgradation closer, the feasibility of upgrading existing microalgal wastewater treatment into immobilized microalgal systems is thoroughly discussed. Eventually, several research directions are proposed toward the future immobilized microalgal system for microalgal wastewater treatment upgrading. Together, it appears that using immobilization for further upgrading the microalgae-based wastewater treatment can be recognized as an achievable alternative to make microalgal wastewater treatment more realistic. The information and perspectives provided in this review also offer a feasible reference for upgrading conventional microalgae-based wastewater treatment.

Integrated strategies for robust growth of Chlorella vulgaris on undiluted dairy farm liquid digestate and pollutant removal

Undiluted dairy farm liquid digestate contains high levels of organic matters, chromaticity and total ammonia nitrogen (TAN), resulting in inhibition to microalgal growth. In this study, a novel cascade pretreatment with ozonation and ammonia stripping (O + S) was employed to remove these inhibitors, and was compared with single pretreatment approach. The optimum parameters for ozonation and ammonia stripping were obtained and the mechanisms of inhibition elimination were investigated. The results show that ozonation contributed to the degradation of non-fluorescent chromophoric organics through the direct molecular ozone attack, which mitigated the inhibition of chromaticity to microalgae, while ammonia stripping relieved the inhibition of high TAN to microalgae. After cascade pretreatment, TAN, total nitrogen (TN), COD and chromaticity were reduced by 80.2 %, 75.4 %, 20.6 % and 75.8 % respectively. When C. vulgaris was cultured on different pretreated digestate, it was found that cascade pretreatment was beneficial for retaining high PSII activity and synergistically improved microalgal growth. The highest biomass increment and productivity achieved 5.40 g L^-1 and 900 mg L^-1 d^-1 respectively in the integration system of cascade pretreatment with microalgae cultivation (O + S + M). After O + S + M treatment, the removal efficiencies of TAN, TN, COD and total phosphorus (TP) were 100 %, 92.8 %, 46.7 % and 99.6 %, respectively. This work provided a promising strategy (O + S + M) for sustainable liquid digestate treatment, along with nutrient recovery and value-added biomass production.

Plastic and Waste Tire Pyrolysis Focused on Hydrogen Production—A Review

In this review, we compare hydrogen production from waste by pyrolysis and bioprocesses. In contrast, the pyrolysis feed was limited to plastic and tire waste unlikely to be utilized by biological decomposition methods. Recent risks of pyrolysis, such as pollutant emissions during the heat decomposition of polymers, and high energy demands were described and compared to thresholds of bioprocesses such as dark fermentation. Many pyrolysis reactors have been adapted for plastic pyrolysis after successful investigation experiences involving waste tires. Pyrolysis can transform these wastes into other petroleum products for reuse or for energy carriers, such as hydrogen. Plastic and tire pyrolysis is part of an alternative synthesis method for smart polymers, including semi-conductive polymers. Pyrolysis is less expensive than gasification and requires a lower energy demand, with lower emissions of hazardous pollutants. Short-time utilization of these wastes, without the emission of metals into the environment, can be solved using pyrolysis. Plastic wastes after pyrolysis produce up to 20 times more hydrogen than dark fermentation from 1 kg of waste. The research summarizes recent achievements in plastic and tire waste pyrolysis development.

New hybrid strategy of the photo-Fered-Fenton process assisted by O3 for the degradation of wastewater from the pretreatment of biodiesel production

The present work aims to fill a scientific gap regarding the treatment of wastewater from the enzymatic pretreatment of biodiesel production (WEPBP), as well as the identification of organic contaminants present in this complex matrix. Different treatment strategies were proposed for the removal of total organic carbon (TOC) and chemical oxygen demand (COD) from WEPBP. The interesting combination of O₃/H₂O₂/UV-Vis and electrocoagulation (EC) process was studied in two setups, with the EC process applied prior to O₃/H₂O₂/UV-Vis and vice versa. Further, the innovative hybrid system based on the photo-Fered-Fenton process with O₃ addition (PEF-Fere-O₃) was preliminarily studied for WEPBP treatment. The hybrid system provided the best results for the WEPBP treatment when the reactor was operated at pH of 4.5, 65 mg O₃ L^-1 and 10000 mg H₂O₂ L^-1, UV-Vis was used as the irradiation source, and the current intensity of 3.0 A. Removals of 45% of TOC and 68.7% of COD were reached within 45 min. Oleic acid, linoleic acid, and Diisooctyl phthalate (DIOP) were the main organic contaminants identified in the WEPBP as determined by Gas Chromatography-Mass Spectrometry (GC-MS) analysis. Acute toxicity assays with the bio indicator Artemia salina were carried out in untreated and treated WEPBP samples, indicating that the PEF-Fere-O₃ treatment decreased the amount of contaminants present in the WEPBP as well as reduced the toxicity levels and increased biodegradability index, suggesting its great potential for the treatment of complex industrial wastewaters.

Microbial Biogas Production from Pork Gelatine

This research describes the results of the anaerobic digestion of gelatine as a potential hydrogen source with heat-shocked inoculum. The concentrations of applied gelatine were of VSS (volatile suspended solids) ranging from 10 g VSS/L to 30 g VSS/L. The initial process pH was 5.5, and, depending on the concentration, reached pH values from 7.5 to 7.8 after 55 days. Although the inoculum was heat-shocked in 30 g VSS/L of collagen, the process that occurred was hydrogenotrophic anaerobic digestion. In gelatine concentrations below 30 g VSS/L, hydrogen production was dominant only during the first 5 days of the experiments. Then, there was a change from dark fermentation to hydrogenotrophic methane production. The optimal hydrogen and methane yields resulted from the concentrations of 10 g VSS/L (7.65 mL ± 0.01 mL H2/g VSS and 3.49 ± 0.01 L CH4/g VSS). Additionally, 10 g VSS/L had the lowest accumulated emission of hydrogen sulphide (10.3 ± 0.01 mL of H2S), while 30 g VSS/L (0.440 ± 0.01mL H2S/g VSS) produced the lowest yield. After a lag time, the hydrogen production and hydrogen sulphide grew with a specific ratio, depending on the concentration. The hydrogen sulphide emission and sulphur added analysis proved that hydrogen sulphide originating from biogas created by bacteria remains longer than that from a substrate.

Role of bulk nanobubbles in removing organic pollutants in wastewater treatment

The occurrence of a variety of organic pollutants has complicated wastewater treatment; thus, the search for sustainable and effective treatment technology has drawn significant attention. In recent years, bulk nanobubbles, which have extraordinary properties differing from those of microbubbles, including high stability and long residence times in water, large specific surface areas, high gas transfer efficiency and interface potential, and the capability to generate free radicals, have shown attractive technological advantages and promising application prospects for wastewater treatment. In this review, the basic characteristics of bulk nanobubbles are summarized in detail, and recent findings related to their implementation pathways and mechanisms in organic wastewater treatment are systematically discussed, which includes improving the air flotation process, increasing water aeration to promote aerobic biological technologies including biological activated carbon, activated sludge, and membrane bioreactors, and generating active free radicals that oxidise organic compounds. Finally, the current technological difficulties of bulk nanobubbles are analysed, and future focus areas for research on bulk nanobubble technology are also proposed.