Beatriz Molinuevo-Salces

Nitrogen transformations under different conditions in open ponds by means of microalgae–bacteria consortium treating pig slurry

Four open ponds inoculated with microalgae-bacteria consortium treating different swine slurries (fresh and anaerobically digested) were evaluated in terms of nitrogen transformation under optimal and real conditions of temperature and illumination. Ammonium complete depletion was not achieved. Ponds operated under real conditions presented lower ammonium removal. Elimination capacities were around 26 mg N/Ld and were subsequently increased with increasing inlet ammonium loading rate. Different nitrogen transformation was observed depending on substrate source. When anaerobically digested slurry was fed to the ponds, nitrification followed by biomass uptake and denitrification were the main nitrogen transformation taking place depending on inlet ammonium loading rate and operational conditions. Ponds fed with fresh slurry exhibited denitrification as the main nitrogen removal mechanism for the pond operated under real conditions while under optimal conditions stripping, denitrification and biomass uptake contributed similarly. Therefore, this study confirmed that the so-claimed nitrogen recovery by microalgae biomass is frequently overestimated.

Performance comparison of two photobioreactors configurations (open and closed to the atmosphere) treating anaerobically degraded swine slurry

The purpose of the study was comparison of two configurations of photobioreactors an open-type photobioreactor open to atmosphere and a tubular type photobioreactor closed to the atmosphere. Organic matter was fairly removed under both configurations at 50-60% and biomass carbon content on dry weight basis accounted for 45%. Both configurations were able to completely exhaust ammonium, however different mechanism removals were responsible for the different influent loads applied. In terms of nitrogen recovery by biomass assimilation, the open configuration ranged 38-47% whereas the closed type presented 31%. It is worth to mention that nitrification-denitrification was taking place under both photobioreactor configurations. Approximately 80% phosphate removal was achieved regardless the configuration and biomass P content was slightly higher in the closed-type reactor. For nutrient recycling, biomass harvesting is described as the key issue of this technology. Nevertheless, the closed configuration highlighted the great potential of the biofilm formation by retaining 96% of the total biomass produced.

Anaerobic co-digestion of livestock wastes with vegetable processing wastes: A statistical analysis

Anaerobic digestion of livestock wastes with carbon rich residues was studied. Swine manure and poultry litter were selected as livestock waste, and vegetable processing waste was selected as the rich carbon source. A Central Composite Design (CCD) and Response Surface Methodology (RSM) were employed in designing experiments and determine individual and interactive effects over methane production and removal of volatile solids. In the case of swine manure co-digestion, an increase in vegetable processing waste resulted in higher volatile solids removal. However, without a proper substrate/biomass ratio, buffer capacity of swine manure was not able to avoid inhibitory effects associated with TVFA accumulation. Regarding co-digestion with poultry litter, substrate concentration determined VS removal achieved, above 80 g VSL(-1), NH(3) inhibition was detected. Statistical analysis allowed us to set initial conditions and parameters to achieve best outputs for real-scale plant operation and/or co-digestion mixtures design.

Anaerobic co-digestion of livestock and vegetable processing wastes: Fibre degradation and digestate stability

Anaerobic digestion of livestock wastes (swine manure (SM) and poultry litter (PL)) and vegetable processing wastes (VPW) mixtures was evaluated in terms of methane yield, volatile solids removal and lignocellulosic material degradation. Batch experiments were performed with 2% VS (volatile solids) to ensure complete conversion of TVFAs (total volatile fatty acids) and to avoid ammonia inhibition. Experimental methane yields obtained for the mixtures resulted in higher values than those obtained from the sum of the methane yields from the individual components. VPW addition to livestock wastes before anaerobic digestion also resulted in improved VS elimination. In SM-VPW co-digestions, CH4 yield increased from 111 to 244 mL CH4 g VS added(-1), and the percentage of VS removed increased from 50% to 86%. For PL-VPW co-digestions, the corresponding values were increased from 158 to 223 mL CH4 g VS added(-1) and from 70% to 92% VS removed. Hemicelluloses and more than 50% of cellulose were degraded during anaerobic digestion. Thermal analyses indicated that the stabilization of the wastes during anaerobic digestion resulted in significantly less energy being released by digestate samples than fresh samples.

Ultrasound-Enhanced Biogas Production from Different Substrates

Among the biofuel production processes using different substrates, the biogas generation process is one of the simplest. Compared with bioethanol or biodiesel production processes, anaerobic digestion is a process where all the organic matter (carbohydrates, lipids and proteins) can be biologically degraded for methane production. Biological degradations of those polymeric substrates are carried out by several enzymes during the first stage of hydrolysis. Nevertheless, due to the substrates physical state, microbial degradation is frequently hampered. Substrate pretreatment enhances the performance of anaerobic digestion by improving the bioavailability of the substrate for anaerobic digestion and thus accelerating the hydrolysis step. Appropriate methods are currently under development in order to increase accessibility of the enzymes to the materials and therefore optimise the ultimate methane production. The present chapter is dedicated to providing a review of ultrasound pretreatment applied to different substrates (lignocelullosic materials, manures, sludge and microalgae). The advantages and constraints, that ultrasound pretreatment exhibit towards biogas production, are discussed and compared with other pretreatment methods.

Key factors influencing the potential of catch crops for methane production

Catch crops are grown in crop rotation primarily for soil stabilization. The excess biomass of catch crops was investigated for its potential as feedstock for biogas production. Ten variables affecting catch crop growth and methane potential were evaluated. Field trials and methane potential were studied for 14 different catch crops species, with 19 samples harvested in 2010 and 36 harvested in 2011. Principal component analysis was applied to the data to identify the variables characterizing the potential for the different catch crops species for methane production. Two principal components explained up to 84.6% and 71.6% of the total variation for 2010 and 2011 samples, respectively. Specific methane yield, climate conditions (rainfall and temperature) and total nitrogen in the biomass were the variables classifying the different catch crops. Catch crops in the Brassicaceae and Graminaceae botanical families showed the highest methane yield. This study demonstrates the importance of the crop species when choosing a suitable catch crop for biogas production.

Gas-Permeable Membrane Technology Coupled With Anaerobic Digestion for Swine Manure Treatment

This study was aimed at evaluating gas-permeable membrane technology (N-recovery) coupled with anaerobic digestion for the treatment of swine manure. For this purpose, 66.7% of the initial total ammoniacal nitrogen contained in centrifuged swine manure (SM) was first recovered by an e-PTFE gas-membrane as an ammonium sulfate solution. The resultant manure effluent with reduced ammonia (ATM) was evaluated as anaerobic digestion (AD) substrate. It was compared with AD using the initial swine effluent (SM) without the N-recovery step (control). An organic loading rate (OLR) of 2.8 ± 0.5 g TCOD L-1 day-1 was established to ensure a stable process when working at semi-continuous mode. Regardless of the operation mode, methane yields of 105 ± 2 mL CH4 g TCOD -1 were obtained for ATM. The combined treatment resulted in an organic matter removal efficiency of 68.6%. Initial TCOD accounted for 54.69 g L-1. The results prove that it is feasible to combine gas-permeable membrane technology and anaerobic digestion for the treatment of swine manure, contributing to ammonia emissions mitigation and sustainable livestock waste treatment. Moreover, by means of this technology combination, a variety of valuable products is obtained, namely sustainable energy in the form of methane and fertilizers.

Recovery of Protein Concentrates From Microalgal Biomass Grown in Manure for Fish Feed and Valorization of the By-Products Through Anaerobic Digestion

The recovery of proteins from microalgae is gaining special attention for animal feed applications especially for fish feed, as the costs of aquaculture feeds represent between 40-70% of the costs of the fish produced. Besides, the use of pig manure to growth microalgae biomass could contribute to manure bioremediation and therefore to reduce the environmental impacts of its storage. The objective of this study was to recover protein concentrates from microalgal biomass grown in pig manure, paying especial attention to the quality of the extracted proteins that can be used as feed source for fish, and to the amino acids composition, essential amino acids content and availability. Methane potential of the by-products obtained after protein recovery was also determined in order to fully apply the biorefinery concept to valorize the resulting biomass. Results showed a maximum protein recovery of 54.5 ± 3.2% from initial microalgal biomass. Protein content in the protein concentrate accounted for 84.5 g protein/100 g biomass in total solids (TS) basis. In the case of the amino acids profile from protein concentrate, essential amino acids accounted for 47.5 g /100 g amino acids in TS basis. After protein recovery, the resulting by-products named spent and liquid fraction were anaerobically digested in batch assays, obtaining a maximum methane production of 181 mL CH4/g VS added.