Wastewater Management in Citrus Processing Industries: An Overview of Advantages and Limits

Citrus-processing industries produce large volumes of wastewater (CPWW). The large variability of these volumes coupled to physicochemical characteristics of CPWW determine severe constraints for their disposal due to both economic and environmental factors. To minimize the management costs and prevent the negative ecological impacts of CPWW, several systems have been proposed and adopted. However, all these treatment/valorization routes have many issues that are not yet thoroughly known by the scientific community and stakeholders of the citrus-processing chain. This paper reports an overview of the possible treatment/valorization opportunities for CPWW: intensive biological treatment, lagooning, direct land application, energy conversion, and biorefinery uses for the extraction of added-value compounds. Advantages and constraints are presented and discussed, and the following conclusions are achieved: (i) there is not a unique solution for CPWW treatment, since the best management system of CPWW must be chosen case by case, taking into account the quality/quantity of the effluent and the location of the transformation industry; (ii) the adoption of a biorefinery approach can increase the competitiveness and the further development of the whole citrus sector, but the cost of novel technologies (some of which have not been tested at real scale) still limits their development

Effects of Ammonia Stripping and Other Physico-Chemical Pretreatments on Anaerobic Digestion of Swine Wastewater

In order to overcome anaerobic digestion (AD) inhibition due to the large nitrogen content of swine wastewater (SW), air stripping (AS) and other chemical and physical pretreatments were applied on raw SW before AD. The efficiency of these pretreatments on both ammonia removal—recovering ammonia salts to be used as fertilizers in agriculture—and the increase of methane production were assessed in batch tests. Since the pH, temperature, and air flow rate heavily influence AS efficiency and the composition of treated SW, these parameters were set individually or in combination. In more detail, the pH was increased from the natural value of SW to 8 or 10, temperature was increased from the room value to 40 °C, and the air flow rate was increased from zero to 5 Lair LSW−1 min−1. AS was generally more efficient at removing ammonia (up to 97%) from raw (non-treated) SW compared to the other treatments. However, the tested pretreatments were not as efficient as expected in increasing the biogas production, because the methane yields of all pretreated substrates were lower (by about 10–50%) to compared raw SW. The inhibitory effect on AD could have been due to the lack of nutrients and organic matter in the substrate (due to the excessive removal of the pretreatments), the concentration of toxic compounds (such as metal ions or furfural due to water evaporation), and an excess of alkali ions (used to increase the pH in AS). Overall, AS can be considered a sustainable process for the recovery of ammonium sulphate and the removal of other polluting compounds (e.g., organic matter) from SW. Conversely, the use of AS and other chemical and/or thermal processes tested in this study as pretreatments of SW before AD is not advised because these processes appear to reduce methane yields

Scenarios of Bioenergy Recovery from Organic Fraction of Residual Municipal Waste in the Marche Region (Italy)

In the Marche Region (Central Italy), the residual municipal waste (RMW) is commonly processed in mechanical biological treatment (MBT) systems. In these systems, following a first mechanical selection, the undersize organic fraction from RMW (us-OFRMW) undergoes a partial aerobic biological treatment before being landfilled as a biostabilised fraction (bios-OFRMW) without dedicated energy or material recovery. Alternative us-OFRMW management scenarios have been elaborated for this region, at both present (reference year 2019) and future (reference year 2035) time bases. In the first scenario, the potential bioenergy recovery through anaerobic digestion (AD) from the us-OFRMW was evaluated. The second scenario aimed at evaluating the residual methane generation expected from the bios-OFRMW once landfilled, thus contributing also to the potential environmental impact connected with landfill gas (LFG) diffuse emissions from the regional landfills. The diversion to AD, at the present time, would allow a potential bioenergy recovery from the us-OFRMW equal to 4.35 MWel, while the alternative scenario involves greenhouse gas (GHG) emissions equal to 195 kg CO2 eq. per ton of deposited bios-OFRMW. In the future, the decreased amount of the us-OFRMW addressed to AD would still contribute with a potential bioenergy recovery of 3.47 MWel

Semi-Continuous Anaerobic Digestion of Orange Peel Waste: Effect of Activated Carbon Addition and Alkaline Pretreatment on the Process

The valorization of orange peel waste (OPW) is sought worldwide mainly via anaerobic digestion. A common problem encountered during the biological treatment is the seasonality of its production and the presence of d-Limonene. The latter is a typical anti-microbial compound. This work aims to evaluate the effect of the use of granular activated carbon (GAC) combined with alkaline pretreatment to enhance methane generation during semi-continuous anaerobic digestion of OPW. The experimental design consisted of two groups of experiments, A and B. Experiment A was designed to verify the maximum OPW loading and to assess the effect of pH and nutrients on the process. Experiment B was designed to study the effect of alkaline pretreatment alone and of alkaline pretreatment aided by biochar addition to the process. Apart from the methane yields, the d-Limonene contents were measured in all experiments. The preliminary results showed that OPW alkaline pretreatment after the addition of a moderate amount of GAC can render anaerobic digestion of OPW sustainable as long as the organic loading does not exceed 2 gVS·L−1·day−1 and nutrients are supplemented. The experiment in which GAC was added after alkaline pretreatment resulted in the highest methane yield and reactor stability

Environmental assessment of different residual municipal waste managements in the Marche Region (Central Italy) before and during the COVID19 pandemic

The SARS-CoV-2 virus has been deeply and worldwide affecting people daily life as well as ordinary procedures in all working fields since when, at the beginning of 2020, the World Health Organisation (WHO) declared the pandemic status. In addition of the social problems related to the virus (such as the lack of human interaction, the difficulty to receive adequate assistance), the pandemic has also changed people habits and, as consequence, the quality and quantity of municipal waste (MW) produced. Moreover, the presence of waste streams generated from people infected by SARS-CoV-2 posed the question on how to manage these potentially hazardous wastes. Therefore, the pandemic also influenced and modified the MW management practices. Under this perspective, this study aimed to (i) quantitatively analyse and compare the residual municipal waste (RMW) produced before (reference year, 2019) and during (reference year, 2020) the pandemic and (ii) evaluate and compare the environmental impact (by the Life Cycle Assessment, LCA, method) of the different applied waste management strategies in the periods pre- and post-COVID19. Specifically, two provincial districts (hereafter indicated as P1 and P2, respectively) of the Marche Region (Central Italy, Adriatic Seaside) were chosen because of the data availability and the different RMW management during the pandemic period

Evaluation of Electrospun Self-Supporting Paper-Like Fibrous Membranes as Oil Sorbents

Presently, adsorption/absorption is one of the most efficient and cost-effective methods to clean oil spill up. In this work, self-supporting paper-like fibrous membranes were prepared via electrospinning and carbonisation at different temperatures (500, 650 or 800 °C) by using polyacrylonitrile/polymethylmethacrylate blends with a different mass ratio of the two polymers (1:0, 6:1 or 2:1). After morphological and microstructural characterisation, the as-produced membranes were evaluated as sorbents by immersion in vegetable (sunflower seed or olive) and mineral (motor) oil or in 1:4 (v:v) oil/water mixture. Nitrogen-rich membrane carbonised at the lowest temperature behaves differently from the others, whose sorption capacity by immersion in oil, despite the great number of sorbent and oil properties involved, is mainly controlled by the fraction of micropores. The encapsulation of water nanodroplets by the oil occurring during the immersion in oil/water mixture causes the oil-from-water separation ability to show an opposite behaviour compared to the sorption capacity. Overall, among the investigated membranes, the support produced with 2:1 mass ratio of the polymers and carbonisation at 650 °C exhibits the best performance both in terms of sorption capacity (73.5, 54.8 and 12.5 g g−1 for olive, sunflower seed and motor oil, respectively) and oil-from-water separation ability (74, 69 and 16 for olive, sunflower seed and motor oil, respectively)

VOLATILE ORGANIC COMPOUNDS FROM GREEN WASTE ANAEROBIC DEGRADATION AT LAB-SCALE: EVOLUTION AND COMPARISON WITH LANDFILL GAS

The chemical composition of volatile organic compounds (VOCs) in landfill gas from municipal waste (MW) landfills primarily depends on the type of degrading waste. To provide first insights into the relationship between VOC chemistry (in landfill gas) and specific waste components, a lab-scale experiment on anaerobic digestion (AD) of green waste (GW) was carried out. The composition of the released C4+ VOCs was semi-quantitatively determined and indirectly compared to that generally expected for the overall MW landfill gas. The generated biogas from degrading GW during AD time showed up to 29 different VOCs, mainly including terpenes, followed by alkanes, alkenes, cyclics, aromatics, and halogenated compounds. O- and S-substituted compounds were sporadically detected. Overall, speciation and total concentration of VOCs fluctuated over AD time, likely due to changes in microbial populations and metabolism, as well as substrate depletion, during the AD evolution. As expected, VOC speciation in the GW biogas was lower than that of the typical MW landfill gas, since the latter is generated by a large variety of organic and synthetic waste components following different sequential degradation processes. These results highlighted that, when disposed of at MW landfill sites, the specific GW component may (i) potentially concur to the overall odour charge and toxic effects of MW landfill gas and (ii) detrimentally impact the energy exploitation of MW landfill gas by releasing terpenes, aromatics, and halogenated compounds

BIOENERGY FROM GREEN WASTE THROUGH ANAEROBIC DIGESTION: SUBSTRATE, BIOGAS, AND DIGESTATE CHARACTERISATION AT LAB-SCALE

none6noThe green waste (GW), generated from private and public gardens, represents a noticeable stream of the organic fraction of municipal waste (OFMW). At the Italian level, the GW quantitative stream is mainly addressed to composting, instead of being valorise through anaerobic digestion (AD) to recover bioenergy as renewable source. On the other hand, the biogas production through AD poses some technical issues, such as the detailed knowledge and comprehension of the biogas composition and its evolution during the AD process; and the consideration of the characteristics of the substrate and digestate in the overall evaluation of the AD process. In view of these concerns, a biochemical methane potential (BMP) experiment was conducted on GW as substrate in mesophilic conditions at lab-scale. Detailed physico-chemical characterisations of the substrate, inoculum, and digestate were performed, in addition to the ultimate analysis on the GW. Moreover, biogas samples were periodically collected from the headspace of one of the digesters containing the substrate-inoculum mixture for the subsequent chemical characterisation. The findings of this experimental study would allow to better understand the mutual relations among substrate physico-chemical characteristics, AD process and biogas composition evolution, and digestate physico-chemical characteristics.Organized by the Politecnico di Torino - Department of Environment, Land, and Infrastructure Engineering (DIATI), the National Association of Sanitary and Environmental Engineering (ANDIS), and the Italian Group of Sanitary and Environmental Engineering (GITISA)noneAdele Folino, Antonio Randazzo, Franco Tassi, Fabio Tatano, Sandro de Rosa, Alma GambioliFolino, Adele; Randazzo, Antonio; Tassi, Franco; Tatano, Fabio; de Rosa, Sandro; Gambioli, Alm

Volatile organic compounds (VOCs) from green waste anaerobic digestion: degradation proceeding and sources assessment

Municipal waste (MW) degradation produces a wide range of volatile organic compounds (VOCs) having a potentially detrimental impact on environment and human health. Chemical composition of biogas in MW landfills is the result of contributions from many different waste categories. In this study, a laboratory experiment on anaerobic digestion (AD) of green waste (GW) was performed to investigate the composition of VOCs released in comparison to that of the overall MW biogas. Up to 29 different VOCs were recognized in gas samples from degrading GW during AD time, including terpenes, followed by alkanes, alkenes, aromatics, and halogenated compounds. The latter, as well as part of aromatics were considered xenobiotic compounds. O- and S-substituted compounds represented the minor fraction of VOCs. The presence of toxic VOC pollutants can make GW-biogas potentially harmful if released (without collection, control, and energy recovery) to the environment. Overall, speciation and total concentration of VOCs fluctuated over AD time. The variable compositional features and biogas production rate were likely caused by changes in microbial populations and metabolism during the AD evolution. As expected, VOCs speciation in GW biogas was lower than those identified in typical MW biogas, since the latter is produced by a large variety of organic and synthetic material following different subsequent oxidative degradation processes. These preliminary results suggest that further laboratory experiments carried out using different MW fraction types than GW, and under different chemical-physical and process conditions, could provide useful technical-scientific information to understand and predict the composition and the quantity of biogas produced and eventually released to the atmosphere from individual waste fractions at MW landfill environments