Assessment of nitrification process in a sequencing batch reactor: Modelling and genomic approach.

Nitrification of ammoniacal nitrogen (N-NH4+) to nitrate (N-NO3-) was investigated in a lab-scale sequencing batch reactor (SBR) to evaluate its efficiency. During the nitrification process the removal of N-NH4+ reached 96%, resulting in 73% formation of N-NO3-. A lineal correlation (r2 = 0.9978) was obtained between the concentration of volatile suspended solids (VSS) and the maximal N-NO3- concentration at the end of each batch cycle under stationary state. The bacterial taxons in the initial inoculum were identified, revealing a complex diverse community mainly in the two major bacterial phyla Proteobacteria and Actinobacteria. The FAPROTAX algorithm predicted the presence in the inoculum of taxa involved in relevant processes of the nitrogen metabolism, highlighting the bacterial genera Nitrospira and Nitrosomonas that are both involved in the nitrification process. A kinetic model was formulated for predicting and validating the transformation of N-NH4+, N-NO2- and N-NO3- and the removal of organic and inorganic carbon (TOC and IC, respectively). The results showed how the increase in biomass concentration slowed down the transformation to oxidised forms of nitrogen and increased denitrification in the settling and filling stages under free aeration conditions.

Odor emission assessment of different WWTPs with Extended Aeration Activated Sludge and Rotating Biological Contactor technologies in the province of Cordoba (Spain).

In this study, five urban WWTPs (Wastewater Treatment Plant) with different biological treatment (Extended Aeration Activated Sludge - EAAS; Rotating Biological Contactor - RBC), wastewater type (Urban; Industrial) and size, were jointly evaluated. The aim was twofold: (1) to analyze and compare their odor emissions, and (2) to identify the main causes of its generation from the relationships between physico-chemical, respirometric and olfactometric variables. The results showed that facilities with EAAS technology were more efficient than RBC, with elimination yields of organic matter higher than 90%. In olfactometric terms, sludge managements facilities (SMFs) were found to be the critical odor source in all WWTPs compared to the Inlet point (I) or Post primary treatment (PP), and for seasonal periods with ambient temperature higher than 25 °C. Moreover, the global odor emissions quantified in all SMFs revealed that facilities with EAAS (C-WWTP, V-WWTP and Z-WWTP) had a lower odor contribution (19,345, 14,800 and 11,029 ouE/s·m2, respectively) than for those with RBC technology (P-WWTP and NC-WWTP) which accounted for 19,747 ouE/s·m2 and 80,061 ouE/s·m2, respectively. In addition, chemometric analysis helped to find groupings and differences between the WWTPs considering the wastewater (71.27% of total variance explained) and sludge management (64.52% of total variance explained) lines independently. Finally, odor emissions were adequately predicted from the physico-chemical and respirometric variables in the wastewater (r2 = 0.8738) and sludge (r2 = 0.9373) lines, being pH, volatile acidity and temperature (wastewater line), and pH, moisture, temperature, SOUR (Specific Oxygen Uptake Rate) and OD20 (Cumulative Oxygen Demand at 20 h) (sludge line) the most influential variables.

Kinetics of combined hydrothermal pretreatment and anaerobic digestion of lignocellulosic biomass (pepper plant and eggplant).

A large quantity of lignocellulosic biomass is generated annually across the world which leads to environmental pollution and requires valorization. This study investigated the effect of hydrothermal pretreatment on the anaerobic digestion and co-digestion of the residual pepper plant and eggplant with a focus on kinetics. Two thermal hydrolysis rates were observed, with the optimal conditions for the hydrothermal pretreatment of lignocellulosic biomass being 120°C for 40 min. Subsequently, single and combined biomethanization was successfully carried out in laboratory-scale completely stirred tank reactors at mesophilic temperature (35°C). A high increase in methane production was observed after the pretreatment of the pepper plant and eggplant. The pretreated and co-digested wastes led to an optimal methane yield of 79 ± 23 mL CH4/g VS. The modified Gompertz model was used to fit the cumulative methane production of the pretreated lignocellulosic substrates. The kinetic model adequately reproduced the experimental results and might be considered a useful tool to simulate the biomethanization behaviour of complex organic substrates.

Influence of packing material on the biofiltration of butyric acid: A comparative study from a physico-chemical, olfactometric and microbiological perspective.

The influence of bed material on the odor removal performance of a biofilter was studied. A compost-wood biofilter and a wood biofilter were treated with a gaseous stream contaminated with butyric acid and comparatively evaluated at pilot scale using olfactometric, physico-chemical and microbiological approaches. The variables analyzed in both biofilters were correlated with specific families of their microbiota composition. In addition to a higher nutrients content (nitrogen and phosphorus), the compost-wood biofilter registered maximum values in number of aerobic microorganisms (3.6·108 CFU/g) and in aerobic microbiological activity (≈40 mg O2/g VS of cumulative oxygen demand at 20 h). This may explain the higher performance of this biofilter compared to the wood biofilter, withstanding odor loads of up to 1450 ouE/m2·s with odor removal efficiencies close to 100%. The analysis of the microbial community showed that Actinobacteria, particularly the mostly aerobic Microbacteriaceae family, might play an important role in butyric acid degradation and hence reduce odor impact. The multidisciplinary analysis carried out in this work could be a very useful strategy for the optimal design of biofiltration operations.

Anaerobic co-digestion of winery waste: comparative assessment of grape marc waste and lees derived from organic crops.

Grapes are one the world's leading fruit crops, with close to 77 million tonnes harvested per year. Grapes are commonly used to produce wine; a process which generates different wastes such as grape mark waste (skins, seeds and stalks), lees and other residues. This study evaluates the treatment of winery waste derived from ecological cultivation by anaerobic digestion to produce energy in the form of methane. Grape marc waste, Verdejo and Pedro Ximenez (PX) wine lees were digested under stable conditions at mesophilic conditions. The PX lees showed the highest methane yield production (433 LSTP CH4/kg VS) with a maximum OLR of 4.58 kg VS/m3·d. In the evaluated range the process was stable with a range of biodegradability of 51-79%. Due to different types of winery waste are generated at consecutive stages of the main production process, the sequential treatment of PX lees, Verdejo lees and grape marc waste in the same anaerobic digester could be an interesting option. This procedure would facilitate the management of the residual streams generated in wineries during the year and promotes the circular economy in the Montilla-Moriles Protected Designation of Origin.

Integral evaluation of granular activated carbon at four stages of a full-scale WWTP deodorization system.

Odor emissions from wastewater treatment plants (WWTPs) have always been a public concern. In this work, the physico-chemical, olfactometric and textural characterization of granular active carbon (GAC) used by an urban WWTP as a deodorization system, as well as the chromatographic quantification of the retained odoriferous compounds, have been carried out. These techniques have allowed an integral evaluation of the contaminated GAC and the characterization of the retained gaseous emission from four different stages of the wastewater treatment (pretreatment header: GAC-1; sand and fat removal: GAC-2; sludge thickening: GAC-3; sludge dehydration: GAC-4). A larger amount and variety of retained odoriferous compounds were found in GAC samples from the wastewater line deodorization (GAC-1 and GAC-2) after the same operation time (one year), GAC-1 being the adsorbent bed that retained the highest mass of volatile compounds (approximately 150µg/g GAC). Furthermore, some variables such as the removed specific odor concentration and free micropore volume were inversely correlated (R2=0.9945). The analysis of odor contribution showed that sulfur-containing compounds were the major odor contributors (61-97%). However, hydrogen sulfide cannot be considered a key odorant in this particular WWTP, since the elimination of this compound does not reduce the significant contribution of other (organic) sulfur compounds to the global odor (especially dimethyl disulfide). Consequently, multi-technical analysis might be a suitable alternative to better understand odor removal by GAC adsorption.

Interactive impacts of boron and organic amendments in plant-soil microbial relationships.

Water shortage and low organic carbon content in soil limit soil fertility and crop productivity. The use of desalinated seawater is increasing as an alternative source of irrigation water. However, it has a high boron (B) content that could cause toxicity in the plant-soil microbial system. Here, we evaluated the responses of the soil microbiota and lemon trees to 3 irrigation B doses (0.3, 1, and 15 mg L-1) under two types of soil management (conventional, CS; and organic, OS) in a 180-days pot experiment. High B doses promoted B accumulation in soil, reaching harmful concentrations that affected soil biodiversity. Our results suggest a close interaction between B and organic labile fractions that increased B availability in soil solution. Besides, B addition to soil impacted on microbial biomass. The bacterial community showed sensitivity to the B dose. Organic amendment did not increase B soil adsorption but it favored B plant uptake. The highest B dose had a detrimental impact on plant physiology, finally resulting lethal for the plants. Our study provides a comprehensive assessment of the microbes-plant interactions in soils irrigated with water with high B content. This will be fundamental in the design of future fertirrigation strategies.

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 ouE/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 ouE/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.

Environmental performance of an industrial biofilter: Relationship between photochemical oxidation and odorous impacts.

Biological techniques are widely used to treat gaseous streams derived from waste treatment plants. The generation of volatile organic compounds (VOCs) is one of the principal pollution sources in composting facilities from which nuisance odours are released. In addition, the generation of photochemical smog with other gases such as NOX can produce ozone at ground level due to their photochemical ozone creation potential (POCP). In this work, the performance of an industrial biofilter was evaluated from an environmental point of view. Specifically, this study evaluated the potential impact in terms of photochemical oxidation and odour emission derived from composting in a vessel under four different aeration conditions. Gas chromatography-time-of-flight mass spectrometry (GC-TOFMS) was used to perform the chemical characterisation of the gaseous streams, while dynamic olfactometry was used to carry out the sensorial analysis. A total of 95 compounds belonging to 12 different families of VOCs were selected. Principal component analysis revealed the influence of each VOC family on each impact category and explained 88% of the total variance. Multivariate regression was used to study the correlation between photochemical oxidation and odour impact, which has never been reported before. The correlations obtained (r ≥ 0.97) evidenced the direct relationship between these two impacts. Photochemical oxidation and odour emission were proven to be important environmental impacts derived from composting facilities, whose abatement might be carried out by biofiltration systems.

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 ouE/m3) in comparison with the lowest concentration of EP (4.7% EP: 9214 and 14720 ouE/m3) or without the addition of EP (reference composting pile: 10200 and 22500 ouE/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.

Optimizing the selection of organic waste for biomethanization.

This study evaluates the feasibility of using simultaneous mass balances of different nutrients as a tool for optimizing feeding composition in anaerobic digestion. Different ratios, among them total chemical oxygen demand/total Kjeldahl nitrogen (TCOD/TKN) and soluble chemical oxygen demand/TCOD (SCOD/TCOD), were assessed. The TCOD/total volatile solids (TVS) ratio was 1.73 kg O2/kg TVS, while, with the exception of the sewage sludge, pig slurry and animal wastes, a linear relationship was established between phosphorus and nitrogen (0.06 kg P/kg TKN (R2 = 0.9045)). The study was applied to different mixtures of waste (cucumber, quince, tomato, strawberry waste, vinasse, glycerol, tomato plant, pig slurry, sewage sludge, fish waste, landfill leachate and viscera). The mass balance was performed for 50 mixtures chosen at random, containing three different wastes. After evaluating the theoretical optimal values determined by the mass balances, the most promising data were compared with the experimental results of the anaerobic co-digestion of one of the three waste mixtures. As predicted by the mass balances, the codigestion of glycerol, strawberry extrudate and fish waste (41:54:4 in VS) improved methane production to a maximum value of 0.308 m3 CH4/kg TVSadded for an organic loading rate of 0.62-4.26 kg TVS/m3·d.

Full-scale composting of sewage sludge and market waste: Stability monitoring and odor dispersion modeling.

The aim of this study was to assess the odor immission derived from full-scale composting of different abundant and highly pollutant organic waste: sewage sludge with bulking agent (SL), sewage sludge pretreated through anaerobic digestion and supplemented with bulking agent (SL-AD), and market waste with olive leaves (MW-OL). The combination of dynamic olfactometry and Gaussian dispersion modeling allowed both the quantification of odor emissions from each waste and the evaluation of their global odorous impact in nearby urban areas. Wind speed, summer and winter seasons, and atmospheric conditions were considered in the dispersion model. The results revealed that high wind speed (2.6 m/s) increases the global odor immission in summer season, independently of atmospheric stability. However, the maximum odor immission concentration recommended for composting process was not exceeded in any case, which depends on each country/region. The experimental results also enable to evaluate the influence of several physico-chemical variables on odor emissions derived from composting. The removal of nitrogen and volatile solids was the main cause for odor generation. Moreover, the microbiological activity of each substrate was monitored throughout the process and different percentages of biodegradability were quantified depending on the type of substrate and pretreatment applied.

Monitoring of the composting process of different agroindustrial waste: Influence of the operational variables on the odorous impact.

Composting is a conventional but economical and environmentally friendly way to transform organic waste into a valuable, organic soil amendment. However, the physico-chemical characterization required to monitor the process involves considerable investment in terms of cost and time. In this study, 52 samples of four compostable substrates were collected randomly during the composting process and analyzed physico-chemically. The physico-chemical characterization was evaluated and reduced by principal component analysis (PCA) (PC1 + PC2: 70% variance). Moreover, a study of the relationship between odor and the raw material and odor and the operational variables was carried out at pilot scale using PCA and multivariate regression. The substrates were grouped by PCA (PC1 + PC2: 87% variance). The odor emission rate (OER) and dynamic respirometric index (DRI) were found to be the most influential variables in the sample variance, being relevant to identify the different emission sources. Dynamic respirometry and multivariate regression could be suitable tools to predict these odor emissions for the majority of compostable substrates, identifying successfully the emission source.

Application of ATAD technology for digesting sewage sludge in small towns: Operation and costs.

In an economic context marked by increasing energy costs and stricter legislation regarding the landfill disposal of wastewater treatment plant (WWTP) sewage sludge, and where biomethanization is difficult to implement in small WWTPs, an efficient alternative is required to manage this polluting waste. This study shows that autothermal thermophilic aerobic digestion (ATAD) is a feasible technique for treating sewage sludge in small- and medium-sized towns. The experiments were carried out at pilot scale on a cyclical basis and in continuous mode for nine months. The main results showed an optimal hydraulic retention time of 7 days, which led to an organic matter removal of 34%. The sanitized sludge meets the microbial quality standards for agronomic application set out in the proposed European sewage sludge directive. An economic assessment for the operation of ATAD technology was carried out, showing a treatment cost of €6.5/ton for dewatered sludge.

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

This study proposes the combination of statistical analysis and a biodegradability test to complement the composition of different wastes in order to find the optimal balance of nutrients for their joint bioconversion. Due to the need to determine the adequate balance of nutrients, the use of alternative techniques to experimental procedures could significantly reduce the cost and time of the process. With this aim, fifteen organic wastes (nine solid and six liquid wastes) were selected and different statistical analyses were performed on the physico-chemical characterization and respirometric variables. Liquid and solid wastes were analyzed separately using principal components analysis (PCA) (PC1 + PC2: 67% of total variance explained for solid substrates and PC1 + PC2: 85% of total variance explained for liquid substrates). The analysis provided considerable information about the predominant chemical composition of each substrate as well as their similarities and deficiencies to identify possible mixtures. In addition to PCA, cluster analyses (CA) were performed to group the substrates and identify the most significant differences between them. The joint evaluation of PCA and CA permitted identifying the optimal waste mixtures (i.e., glycerol-strawberry-fish waste) by correlating the loadings and scores plot, the cluster analysis dendograms and the COD/TKN ratio from the physico-chemical characterization. Moreover, multivariate regression was found to be an appropriate tool for predicting microbiological activity, as well as the soluble available biodegradable organic matter of each substrate. Inorganic carbon (CIC) and total organic carbon (CTOC) were found to be the most influential parameters in the prediction correlation of oxygen consumption and oxygen uptake rate.

Centralized management of sewage sludge and agro-industrial waste through co-composting.

In this research study, the co-composting process of a waste mixture containing strawberry extrudate, fish waste, sewage sludge and bulking agent (SEFW, 190:1:22:90 ratio) was carried out in a dynamic-solid respirometer at pilot scale. The aerobic biodegradability of the mixture was previously ensured in a static-liquid respirometer. The advantages and drawbacks of the SEFW co-composting process were subsequently identified through the determination of respirometric activity and the physical-chemical characterization of the waste, as well as the monitoring of odor emissions. The evolution of the physical-chemical variables showed that pH increased slightly and that the organic matter concentration, expressed as volatile solids (VS, %) or oxidable organic carbon (COXC, %), decreased by around 15% in both cases and by approximately 56% in its biodegradable form (total organic carbon, TOC, %). The low odor emission rate (OER) in the least favorable scenario (the maximum odor generation) during SEFW composting was 1.59 ouE/s, whereas this figure reached 3.52 ouE/s when only the organic fraction of municipal solid waste (OFMSW) was composted. Consequently, the co-composting of SEFW is more favorable in terms of odor emission and permits the simultaneous treatment of different types of waste.

Modelling of composting process of different organic waste at pilot scale: Biodegradability and odor emissions.

The composting process of six different compostable substrates and one of these with the addition of bacterial inoculums carried out in a dynamic respirometer was evaluated. Despite the heterogeneity of the compostable substrates, cumulative oxygen demand (OD, mgO2kgVS) was fitted adequately to an exponential regression growing until reaching a maximum in all cases. According to the kinetic constant of the reaction (K) values obtained, the wastes that degraded more slowly were those containing lignocellulosic material (green wastes) or less biodegradable wastes (sewage sludge). The odor emissions generated during the composting processes were also fitted in all cases to a Gaussian regression with R2 values within the range 0.8-0.9. The model was validated representing real odor concentration near the maximum value against predicted odor concentration of each substrate, (R2=0.9314; 95% prediction interval). The variables of maximum odor concentration (ouE/m3) and the time (h) at which the maximum was reached were also evaluated statistically using ANOVA and a post-hoc Tukey test taking the substrate as a factor, which allowed homogeneous groups to be obtained according to one or both of these variables. The maximum oxygen consumption rate or organic matter degradation during composting was directly related to the maximum odor emission generation rate (R2=0.9024, 95% confidence interval) when only the organic wastes with a low content in lignocellulosic materials and no inoculated waste (HRIO) were considered. Finally, the composting of OFMSW would produce a higher odor impact than the other substrates if this process was carried out without odor control or open systems.

Improvement of anaerobic digestion of sewage sludge through microwave pre-treatment.

Sewage sludge generated in the activated sludge process is a polluting waste that must be treated adequately to avoid important environmental impacts. Traditional management methods, such as landfill disposal or incineration, are being ruled out due to the high content in heavy metal, pathogens, micropolluting compounds of the sewage sludge and the lack of use of resources. Anaerobic digestion could be an interesting treatment, but must be improved since the biomethanisation of sewage sludge entails low biodegradability and low methane production. A microwave pre-treatment at pilot scale is proposed to increase the organic matter solubilisation of sewage sludge and enhance the biomethanisation yield. The operational variables of microwave pre-treatment (power and specific energy applied) were optimised by analysing the physicochemical characteristics of sewage sludge (both total and soluble fraction) under different pre-treatment conditions. According to the variation in the sCOD and TN concentration, the optimal operation variables of the pre-treatment were fixed at 20,000 J/g TS and 700 W. A subsequent anaerobic digestion test was carried out with raw and pre-treated sewage sludge under different conditions (20,000 J/g TS and 700 W; 20,000 J/g TS and 400 W; and 30,000 J/g TS and 400 W). Although stability was maintained throughout the process, the enhancement in the total methane yield was not high (up to 17%). Nevertheless, very promising improvements were determined for the kinetics of the process, where the rG and the OLR increased by 43% and 39%, respectively, after carrying out a pre-treatment at 20,000 J/g TS and 700 W.

Integral valorisation of waste orange peel using combustion, biomethanisation and co-composting technologies.

Although recent research has demonstrated that waste orange peel (WOP) is a potentially valuable resource that can be transformed into high value products, heat generation, biomethanisation and composting might be considered the most feasible alternatives in terms of yield. This study revealed that WOP can be successfully valorised through combustion. However, a previous drying step, which generates hazardous wastewater, is required and harmful NOx are emitted with the flue gases. In contrast, a high yield of renewable methane (280LSTPCH4/kg added COD, chemical oxygen demand) and an organic amendment can be obtained through the thermophilic biomethanisation of WOP following the removal of valuable essential oils from the peel. Co-composting of WOP combined at different proportions (17-83%) with the organic fraction of municipal solid waste (OFMSW) was also demonstrated to be suitable. Moreover, a 37% reduction in odour generation was observed in co-composting of WOP compared to single composting of OFMSW.