Potentialities of biotechnological recovery of methane, hydrogen and carboxylic acids from agro-industrial wastewaters

Simultaneous production of hydrogen-methane and spatial community succession in an anaerobic baffled reactor treating corn starch processing wastewater

Corn starch processing wastewater (CSPW) is a high-strength organic wastewater and biological treatment is considered as the dominant process. The present work investigated the effects of pH on the bioenergy production and spatial succession of microbial community in an anaerobic baffled reactor (ABR) treating CSPW. The results showed that above 90.5% of COD removal and above 16.6 L d^-1 of methane were achieved at the influent pHs of 8.0 and 7.0 under organic loading rate of 4.0 kg COD·m^-3·L^-1 condition. Further decreasing the influent pH to 6.0 resulted in the COD removal decreased to 89.7%. Besides, 9.2 L d^-1 of hydrogen and 13.0 L d^-1 of methane were obtained. There was significant difference in the volatile fatty acids profiles during the variation of pH. Illumina Miseq sequencing showed that Clostridium, Ethanoligenens, Megasphaera, Prevotella and Trichococcus with relative abundance of 2.1%∼28.1% were the dominant hydrogen-producing bacteria in C1. Methanogens (Methanothrix and Methanobacterium) dominated in the last three compartments. Function predicted analysis revealed that the abundance of metabolic-related gene families containing carbohydrate, amino acids and energy in the last three compartments were higher than that in C1. A deduced biodegradation model of CSPW in ABR revealed that the anaerobic sludge in C1 mainly produced hydrogen. Microbial population in C3 was responsible for COD removal and methane production. The redundancy analysis revealed that hydrogen production was highly correlated with some hydrogen-producing bacteria in C1, whereas methane production was positively correlated with microbial group in C2∼ C4.

S/X ratio impacts the profile and kinetics of carboxylic acids production from the acidogenic fermentation of dairy wastewater

The acidogenic fermentation of dairy wastewater (DW) was evaluated for carboxylic acids (CA) production, investigating the influence of substrate/microorganism (S/X) ratio and applying different mathematical models to the bioproduct formation data. The experiments were performed in batch reactors for 28 days, and four S/X ratios were tested (0.8, 1.2, 1.6, and 1.9 gCOD gVSS^-1). The S/X ratio increase did not influence the percentage of DW conversion into carboxylic acids (42-44%), but the productivity was positively affected (100-200% in general). Acetic acid was the CA formed in the highest concentration for all experiments, followed by propionic and butyric acids. Exponential models were better suited to describe this kinetics process. Therefore, according to the estimated kinetic parameters, the S/X ratio 1.6 was more suitable for CA production from acidogenic fermentation of dairy wastewater, in which the concentrations of longer CA, such as propionate and butyrate, were formed in higher quantities. In addition, it was determined a correlation between the S/X ratio and kinetic parameters like degradation/production rate constant (K) and maximum productivity rate (μ_m).

Resource recovery from sugarcane vinasse by anaerobic digestion - A review

The increase in biofuel production by 2030, driven by the targets set at the 21st United Nations Framework Convention on Climate Change (COP21), will promote an increase in ethanol production, and consequently more vinasse generation. Sugarcane vinasse, despite having a high polluting potential due to its high concentration of organic matter and nutrients, has the potential to produce value-added resources such as volatile fatty acids (VFA), biohydrogen (bioH₂) and biomethane (bioCH₄) from anaerobic digestion. The objective of this paper is to present a critical review on the vinasse treatment by anaerobic digestion focusing on the final products. Effects of operational parameters on production and recovery of these resources, such as pH, temperature, retention time and type of inoculum were addressed. Given the importance of treating sugarcane vinasse due to its complex composition and high volume generated in the ethanol production process, this is the first review that evaluates the production of VFAs, bioH₂ and bioCH₄ in the treatment of this organic residue. Also, the challenges of the simultaneous production of VFA, bioH₂ and bioCH₄ and resources recovery in the wastewater streams generated in flex-fuel plants, using sugarcane and corn as raw material in ethanol production, are presented. The installation of flex-fuel plants was briefly discussed, with the main impacts on the treatment process of these effluents either jointly or simultaneously, depending on the harvest season.

Biochemical potential evaluation and kinetic modeling of methane production from six agro-industrial wastewaters in mixed culture

Methane (CH₄) production from anaerobic digestion of solid and liquid agro-industrial wastes is an attractive strategy to meet the growing need for renewable energy sources and promote environmentally appropriate disposal of organic wastes. This work aimed at determining the CH₄ production potential of six agro-industrial wastewaters (AWW), evaluating the most promising for methanization purposes. It also aims to provide kinetic parameters and stoichiometric coefficients of CH₄ production and define which kinetic models are most suitable for simulating the CH₄ production of the evaluated substrates. The AWW studied were swine wastewater (SW), slaughterhouse wastewater (SHW), dairy wastewater (DW), brewery wastewater (BW), fruit processing wastewater (FPW), and residual glycerol (RG) of biodiesel production. RG was the substrate that showed the highest methanization potential. Exponential kinetic models can be efficiently applied for describing CH₄ production of more soluble substrates. On the other hand, logistic models were more suitable to predict the CH₄ production of more complex substrates.

Bioproducts characterization of residual periphytic biomass produced in an algal turf scrubber (ATS) bioremediation system

The transformation of residual biomass from bioremediation processes into new products is a worldwide trend driven by economic, environmental and social gain. The present study aimed to evaluate the potential for obtaining bioproducts of technological interest from the remaining periphytic biomass formed during a bioremediation process with an algal turf scrubber (ATS) system installed in a lake catchment. Different methodologies were used according to the target bioproduct. Analyses were performed by high performance liquid chromatography with diode array detector (HPLC/DAD), gas chromatography mass spectrometry (GC-MS), ultraviolet-visible spectroscopy (UV-VIS) and inductively coupled plasma optical emission spectrometry (ICP-OES). The results demonstrated that the periphytic biomass presented potential since protein (17.7%), carbohydrates (22.4%), total lipids (3.3%) with 3.6 mg mL^-1 of fatty acids, antioxidants (144.5 μmol Trolox eq. g^-1) and chlorophyll a, chlorophyll b and carotenoids (1,719.7 μg mL^-1, 541.2 μg mL^-1 and 317.7 μg mL^-1, respectively) were obtained. Inorganic analysis presented a value of 42.3 ± 2.58% of total ash and metal presence was detected, indicating bioaccumulation. The properties found in periphyton strengthen the possibility of its application in different areas, ensuring bioremediation efficiency.