Multivariate analysis and biodegradability test to evaluate different organic wastes for biological treatments: Anaerobic co-digestion and co-composting

Optimization of lignocellulolytic bacterial inoculum and substrate mix for lignocellulose degradation and product quality on co-composting of green waste with food waste

The present study evaluates the effect of the mixing ratio of substrates and inoculation with lignocellulolytic bacteria on green waste (GW) and food waste (FW) co-composting. A Box-Behnken design was used to simultaneously optimize the lignocellulose degradation (%LD) and end-product quality. The best operational conditions were 4.85*10⁵ CFU g^-1 of Bacillus sp. F3X3 and 1.44*10⁶ CFU g^-1 of Paenibacillus sp. F1A5 with a substrate mixture containing 50% GW, 32.5% unprocessed FW, 2.5% processed FW, 13% sawdust, and 2% phosphate rock; with a C/N ratio of 27. Under these conditions, the %LD was 33% and the end-product has pH 8.3, TOC 22,4%, TN 1,7%, and a germination index of 103%. Therefore, the product complies with quality standards for organic fertilizers. The results of this study allow the identification of appropriate strategies to optimize GW composting, increasing the degradation of lignocellulose and improving the end-product quality.

Composting of Olive Mill Pomace, Agro-Industrial Sewage Sludge and Other Residues: Process Monitoring and Agronomic Use of the Resulting Composts

The viability of co-composting of olive mill pomace added to sewage sludge with other organic residues was evaluated and the agronomic use of the final composts was investigated. Two composting piles at different carbon-nitrogen ratios were performed, in which olive mill pomace (OMP), sewage sludge from vegetable processing (SS), fresh residues from artichoke processing residues (AR), and wheat straw (WS) were used. The two composting piles were placed inside a specially built greenhouse and a turning machine pulled by a tractor was used for turning and shredding the organic matrix (every 6 days) during the process. The humidity and temperature of organic matrices have been monitored and controlled during the entire composting process, which lasted 90 days. The process was also monitored to evaluate the microbiological safety of the final compost. The humidity of both piles was always kept just above 50% until the end of the thermophilic phase and the maximum temperature was about 50 °C during the thermophilic phase. The carbon-nitrogen ratio decreased from 21.4 and 28.2, respectively (initial value at day 1 in Pile A and B), to values ranging from 12.9 to 15.1, both composts that originated from the two different piles were microbiologically safe. During a two-year period, the effects of different types of compost on the main qualitative parameters of processing tomato and durum wheat was evaluated. Five fertilization treatments were evaluated for tomato and durum wheat crops: unfertilized control (TR₁); compost A (TR₂); compost B (TR₃); ½ mineral and ½ compost A (TR₄); and mineral fertilizer commonly used for the two crops (TR₅). Concerning the processing tomato yield, TR₅ and TR₄ showed the best results (2.73 and 2.51 kg, respectively). The same trend was observed considering the marketable yield per plant. The only difference was related to the treatments that included the compost (2.32, 1.77, and 1.73 kg/plant for TR₄, TR₃, and TR₂, respectively). As regards the qualitative parameters of tomato, the highest average weight of the fruits was found in the TR₅, TR₄, and TR₃ treatments (respectively, 73.67 g, 70.34 g, and 68.10 g). For durum wheat, only the protein component was differentiated between treatments. Furthermore, wheat grain yield parameters generally increased by combined application of mineral fertilizer and compost.

Study of the Tagus River and Entrepeñas reservoir ecosystem around the Trillo nuclear power plant using chemometric analysis: Influence on water, sediments, algae and fish

The fluvial and aquatic ecosystem of the Tagus River and Entrepeñas reservoir located in the surrounding of the Trillo nuclear power plant (NPP) was evaluated from 1992 to 2008, considering the physical-chemical characteristics, metal content and radiological activity of the water, sediments, algae and fish. The water of both basins demonstrated pH, conductivity, COD, NO₃^- and DO values within a range considered as good quality and the water quality index (WQI) was found to be within a range of 71-90. Chemometric analysis revealed a shift in the river water (from upstream to downstream) affected by the concentration of salts and metals of natural origin, such as Fe and Al, and slight variations in temperature and radiological activity were detected due to the discharges from the NPP. The hydric conditions contributed to increase or decrease the metal concentration of the river water, the reservoir sediments, algae and fish. Fe and Al were found in higher concentration during drought periods and accumulated in sediments, algae and fish along the river course (from SP1 to SP3). Natural and artificial radionuclides found were ⁴⁰K with an average of 245 Bq/kg in river sediments, 499 Bq/kg in reservoir sediments and 121 Bq/kg in fish, and ⁹⁰Sr with a concentration between 0.40 and 1.30 Bq/kg in sediments. Contamination of the aquatic ecosystem with metals and radionuclides was low according to European legislation. In conclusion, this study provides additional elements aimed at understanding the dynamics of fluvial and lentic ecosystems under the influence of different disturbances.

Biofiltration of butyric acid: Monitoring odor abatement and microbial communities

The objective of this study is to evaluate comparatively the odor removal efficacy of two biofilters operated under different conditions and to identify taxonomically the microbial communities responsible for butyric acid degradation. Both biofiltration systems, which were filled with non-inoculated wood chips and exposed to gas streams containing butyric acid, were evaluated under different operational conditions (gas airflow and temperature) from the physical-chemical, microbiological and olfactometric points of view. The physical-chemical characterization showed the acidification of the packing material and the accumulation of butyric acid during the biofiltration process (<60 days). The removal efficacy was found to be 98-100% during the first 20 days of operation, even at high odor concentration. Changes in the operational temperature increased the odor load factor from 400 to 1400 ou_E/m²·s, which led to the reduction of microbiota in the packing material, and a drastic drop of the odor removal efficacy. However, the progressive increase in gas airflow improved the biodegradation efficacy of butyric acid up to 88% with odor loadings as high as 33,000 ou_E/m³, while a linear relationship between odor inlet load and removal capacity was also found. The analysis of the microbial community showed that Proteobacteria was the most abundant phylum along the biofiltration time (58-92%) and regardless of the operational conditions. Finally, principal component analysis applied to the physical-chemical and microbiological data set revealed significant differences between the two biofilters under study.

Waste to Energy: A Focus on the Impact of Substrate Type in Biogas Production

Anaerobic digestion is an efficient technology for a sustainable conversion of various organic wastes such as animal manure, municipal solid waste, agricultural residues and industrial waste into biogas. This technology offers a unique set of benefits, some of which include a good waste management technique, enhancement in the ecology of rural areas, improvement in health through a decrease of pathogens and optimization of the energy consumption of communities. The biogas produced through anaerobic digestion varies in composition, but it consists mainly of carbon dioxide methane together with a low quantity of trace gases. The variation in biogas composition are dependent on some factors namely the substrate type being digested, pH, operating temperature, organic loading rate, hydraulic retention time and digester design. However, the type of substrate used is of greater interest due to the direct dependency of microorganism activities on the nutritional composition of the substrate. Therefore, the aim of this review study is to provide a detailed analysis of the various types of organic wastes that have been used as a substrate for the sustainable production of biogas. Biogas formation from various substrates reported in the literature were investigated, an analysis and characterization of these substrates provided the pro and cons associated with each substrate. The findings obtained showed that the methane yield for all animal manure varied from 157 to 500 mL/gVS with goat and pig manure superseding the other animal manure whereas lignocellulose biomass varied from 160 to 212 mL/gVS. In addition, organic municipal solid waste and industrial waste showed methane yield in the ranges of 143–516 mL/gVS and 25–429 mL/gVS respectively. These variations in methane yield are primarily attributed to the nutritional composition of the various substrates.

Evaluation of hydrothermal pretreatment for biological treatment of lignocellulosic feedstock (pepper plant and eggplant)

Plant residues are an important source of organic matter that can be degraded by aerobic or anaerobic biological processes. However, due to the presence of lignocellulosic material, these residues are not easily biodegradable. Greenhouse crops, such as pepper and eggplant, generate large amounts of this type of waste after harvesting. In this study, a hydrothermal pretreatment was applied at 120 °C and different times to evaluate the enhancement of C and N solubilization in these residues. The highest solubilization of C was obtained at 40 min, as no significant increases were observed at higher times (100% and 68% for pepper plant [PP] and eggplant [EP], respectively). The solubilization of N shows a linear behavior (PP r² = 0.9670 and EP r² = 0.9395). Aerobic and anaerobic biodegradability were also evaluated, with better results found for the anaerobic digestion of the pretreated substrates. The nutrients balance with anaerobic co-digestion of both pretreated substrates (50:50% wt) improved methane production by 1.4 and 1.8 with respect to the substrates individually.

Co-composting of sewage sludge and eggplant waste at full scale: Feasibility study to valorize eggplant waste and minimize the odoriferous impact of sewage sludge

Sewage sludge and bulking agent with small proportions of eggplant waste (EP) (4.7 and 8.6%) were co-composted at full scale to evaluate the feasibility of their joint valorization and to reduce the odorous impact during composting. In this sense, physico-chemical, respirometric and olfactometric variables were monitored throughout the co-composting process. The physico-chemical variables studied were related to each other to evaluate their effect on the quality of the final product and the odoriferous impact. It was observed that the reduction in nitrogen concentration was not parallel to the removal of organic matter, which influenced the odor concentration emitted. Furthermore, during the hydrolytic stage of the co-composting process, the odor concentration was lower when the agricultural waste content was highest (8.6% EP: 6317 and 8192 ou_E/m³) in comparison with the lowest concentration of EP (4.7% EP: 9214 and 14720 ou_E/m³) or without the addition of EP (reference composting pile: 10200 and 22500 ou_E/m³). Although sewage sludge is more biodegradable than eggplant waste, the co-composting process was carried out under suitable conditions. Approximately 90 days were required to obtain a stabilized compost. Consequently, co-composting might be a suitable alternative to valorize EP and reduce the odoriferous impact of sewage sludge, with the consequent economic, social and environmental benefits.

Multivariate insights of bulking agents influence on co-biodrying of sewage sludge and food waste: Process performance, organics degradation and microbial community

As a prerequisite additive, bulking agent played an essential role on organic wastes biodrying by affecting the organics degradation and microbial consortia. In this study, a series of experiments were conducted to explore the relationships among the type of bulking agents, organics degradation and microbial community evolution. In line with the excellent physiochemical properties, corncob was found to be more desirable for biodrying with more water removal (62.13% vs. 53.70% for sawdust and 51.72% for straw) and higher energy efficiency. Furthermore, different bulking agents showed different biodegradability and affected co-existed organics degradation. In detail, corncob upgraded the amylase and lipase activities, thus promoting the degradation of readily degradable carbohydrates and lipids in feedstocks, which accounted for >60% of the bio-heat sources for water evaporation. In addition, pyrosequencing analysis revealed that Bacillus (>50%) and Ochrobactrum (>40%) were the dominant genera in thermophilic and cooling phases, with degradation capacities of readily degradable substrate and lignocellulose, respectively. And the pathogens, e.g., E. coli and K. pneumonia, were seriously inhibited by high matrix temperatures in corncob trial. These results not only suggested the corncob was a promising bulking agent, but the potential microbial mechanisms for organics degradation were also revealed.