Large volumes of a potentially polluting effluent are generated during oil extraction, denominated production water or produced water (PW). PW is characterised by high concentrations of contaminants, such as COD, nitrogen and phosphorus, heavy metals, hydrocarbons and others. This review aims to analyse ex situ biological treatment methods using microorganisms for PW. There are several consolidated physical and chemical treatments of PW. However, they present high operation costs and may raise the final value of the product. Thus, the biological treatment of PW performed ex situ by microorganisms has been the goal of research in recent decades, in order to develop an efficient and less costly process when compared to conventional treatments, resulting in microbial biomass and clean water. Ex situ biological treatment by microorganisms is carried out in acclimated bioreactors, with environmental (salinity, pH, temperature and light intensity (for microalgae)), nutritional (macro and micronutrients, and contaminants concentration to avoid nutrient limitation or substrate inhibition, mainly caused by hydrocarbons) and operating adaptations (type of bioreactor, class of microorganisms, treatment time and mode of operation (batch or continuous)) to maximize the treatment performance, which is promising reaching high removal rates of total oil and greases, nitrogen, phosphorus, metals and other contaminants. Bacteria are the most applied microorganisms even though microalgae, yeasts and filamentous fungi be tested in the last decade. Advantages and limitations of each class of microorganisms are presented in this review, and more research and technological development are expected in the future for this research topic.
The growing acceptance of hydrogen as a suitable substitute for fossil fuel makes it a resource that can be completely utilized in decarbonizing the environment. It is recognized as the cleanest and best fuel that can expedite the mitigation of the presence of anthropogenic greenhouse gas emissions in the environment because of its high energy density, good calorific value, and significant environmental benefits. It is distinct from other fuels in that it may be created through biological, thermochemical, and electrochemical processes and in that wastes can be used as a feedstock for its production. This paper focuses on reviewing biohydrogen production from wastewater. It discusses techniques that could be harnessed to produce biohydrogen from wastewater, factors that can be improved to enhance the performance of this gaseous fuel, an overview of bioreactors, and the technical challenges associated with the use of biohydrogen produced from wastewater. It also provides an economic overview of biohydrogen production from wastewater and the prospects of using this waste-to-fuel technique to address both energy and environmental concerns in developing areas such as Africa. This work established that using wastewater for biohydrogen production is economically friendly and also gives considerable hydrogen yield. The cost-to-benefit analysis varies depending on the type of wastewater used, the biological process involved, and the amount of hydrogen produced. The average investment cost varies around a range of 0.4–18.5 USD/m3 of biohydrogen. The revenue obtained by using wastewater for biohydrogen production can be as high as 4.2 million USD on an annual basis for a reactor volume of 500 m3, which produces about 448,000 kg of H2 yearly. Deploying low-cost and effective bioreactors, optimizing available hydrogen production techniques, and addressing the storage issues scourging biohydrogen are suggested ways of improving its potential.
Microcystis aeruginosa is a common freshwater cyanobacterium inflicting a potentially detrimental effect on aquatic and terrestrial life forms due to their bloom formation and production of hepatotoxin called Microcystin. Although several cases of human and animal poisoning associated with Microcystis aeruginosa bloom have been reported worldwide, there are only a few studies or bloom reports, particularly in Indian aquatic systems. Frequent occurrences of such toxic Microcystis blooms are a threat to water quality as well as the health of humans and animals. Increased cultural eutrophication and varying climatic conditions have intensified the incidents of Microcystis blooms in different waterbodies, most of which remain undocumented. The complexity of the ecology of bloom formers and variables affecting bloom formation and toxin production limits the complete understanding of microalgal blooms. The potential environmental and health risks caused by Microcystis blooms and their toxins make them an ecologically and economically important species. Hence, a holistic understanding of the effects of Microcystis blooms, dynamics, and their toxicity is inevitable. Therefore, this review recapitulates the toxic freshwater cyanobacteria Microcystis, briefly emphasising the occurrence of Microcystis bloom reports along the Indian waters, factors catalysing the bloom formation and its related toxicity studies. This review further provides an overview of the life cycle of Microcystis species, the toxic effects of Microcystin and its mode of action.
Flood disaster has always been the key direction of urban governance and the real-time optimization of urban drainage system has become an important solution. At present, the control of gates in urban flood control system is dominated by rule-based control (RBC), while the research on real-time optimization control (RTC) based on gate opening is relatively few. This paper develops a real-time reservoir optimization model (RTROM) to solve the problem of urban flash flood control. The gate opening was discretized at an interval of 0.1 m as a decision variable, and the differential evolution algorithm (DE) was used to calculate the objective function of this study to obtain the optimal control strategy describing the operation of urban flood control system. The model was tested in the Jingdian Lake area in Fuzhou, China. The results show that in practice, the model can reduce the upstream flood flow by 48.2 m3/s, but also increase the discharge flow after a delay of 17 h. Jingdian Lake can store up to 126,000 m3 of floodwater, and the storage capacity utilization rate has reached 68.5%. It shows that RTROM can maximize the effect of regional lake flood control. More importantly, it effectively lowered the water level of the downstream Qintin Lake by 0.53 m, reducing the flood risk faced by the Qintin Lake. Compared with rule-based control (RBC) model, RTROM is more effective in reducing urban flooding and can provide optimal operation strategies for the real-time operation of urban drainage systems.
In this study, microalgae were isolated and identified as Tetradesmus obliquus from the Northeast of Brazil, according to its morphological and molecular characterization. Its potential to be used in bioremediation of effluents was evaluated in the treatment of dairy wastewater through mixotrophic cultivation in open system. Experimental conditions were tested in different whey concentrations (0.5, 1, 2 and 4% v/v) and light intensities (25, 50, 100 and 200 µmol m−2 s−1) for 14 days. The whey was characterized with high contents of chemical oxygen demand (COD) (52,886 mg L−1), total nitrogen (TN) (1563 mg L−1) and total phosphorus (TP) (663.5 mg L−1). It was found that the presence of exogenous microorganisms did not inhibit microalgae growth and they alone did not treat efficiently the wastewater (control). Dry cell weight (microbial sludge) reached values between 200 and 600 mg L−1. Increasing whey concentration was positive for COD removal capacity in terms of the amount removed, reaching up to 80% of removal rate, even though be better to work up to 1% of diluted whey (legislation requirements of discharge). Higher TN (83–94%) and TP (almost 100%) removal rates were obtained when higher light intensities (100 and 200 µmol m−2 s−1) and lower concentrations (0.5 and 1% of whey) were applied. Nitrogen and phosphorus content in biomass varied between 4–11% and 0.5–1.4% (dry cell weight), respectively.
As the global demand for ginger products continues to increase due to its medicinal and culinary properties, concerns arise regarding the loss of soil carbon (C) caused by agricultural management practices. It is crucial to understand the impact of these practices on soil C changes, especially in ginger rotation cropping systems. The goal of this study was to estimate the soil C changes resulting from management practices of ginger rotation cropping systems, and understand their influence on greenhouse gas (GHG) emissions of pickled ginger. The Intergovernmental Panel on Climate Change (IPCC) Tier 1 method with modification was used to predict the soil C changes of two different 4-year rotation cycles, one of maize-ginger rotation relative to the reference of maize-pumpkin rotation, and the other of upland rice-ginger rotation relative to the reference of upland rice-vegetable rotation for 20 years of cultivation. From the results, ginger rotation cropping systems could lead to soil C changes, ranging from − 0.02 to 0.31 Mg C ha−1 yr−1, compared to − 2.02 Mg C ha−1 yr−1 when converting forests to ginger plantations. Consequently, the net GHG emissions of pickled ginger varied from − 6.71% to 0.00% for ginger rotations and 46.33% for converting forest to cultivate ginger. The waste disposal was the primary source of GHG emissions of pickled ginger. Sustainable waste management practices could potentially reduce GHG emissions by over 60%. Implementing certain practices, such as reduced tillage, keeping all crop residue on the field, and avoiding deforestation to ginger plantations, could increase soil C sequestration.
The increasing demand for energy and the growing concerns over environmental issues have prompted researchers to explore alternative energy sources, such as biodiesel. Biodiesel is a renewable, non-toxic, and biodegradable fuel derived from vegetable oils, animal fats, and waste oils, making it a sustainable energy source. This study aimed to optimize the recovery of transesterifiable oil from industrial fats, oil, and grease (FOG) esterified with an H2SO4 catalyst extracted from discarded lead-acid batteries. In recovering the oil, a thermal process was employed to extract it from the raw FOG, followed by esterification with sulfuric acid derived from lead-acid batteries. Central composite design (CCD) of the response surface methodology (RSM) was used to optimize the operating variables, including methanol-to-oil ratio, catalyst loading, temperature, and reaction time. The optimized conditions resulted in a 96.47 ± 0.68% transesterifiable oil recovery using an 8:1 methanol-to-oil molar ratio, 8 v% of H2SO4 catalyst, and 4 h of reaction time at 50 °C. The recovered oil was characterized for various parameters: density, pH, free fatty acid (FFA) level, fatty acid profile, and functional groups. The results indicated that the recovered oil could be a suitable raw material for biodiesel production, as it possessed desirable properties such as low FFA content and a high percentage of unsaturated fatty acids.