Utilization of Liquid Anaerobic Digestate using Recirculating Hydroponic Planting System

Anaerobic digestion of municipal and animal wastes provides a potentially important means of producing energy sustainably. The reliable production of methane from anaerobic digestion requires that bacteria metabolise municipal and agricultural wastes to produce mainly carbon dioxide and methane. Our model uses Monod based kinetics and is complex since the biomass concentration growth is inhibited with the increase in substrate. The production of methane depends on the number of methanogenic bacteria; there is evidence from previous chemostats experiments that there is a time delay in population number of these cells to respond to changes in substrate concentrations. In this article we focus on determining the dynamical response of the methane production rate under different dynamics of feed conditions and temperatures. Since there is a delay in the methane bacteria mass response, we include the effects of the delay on the dynamics of the system based on modification of kinetics in a simple fermentation anaerobic model. We compare the dynamics of the system with and without delay to show the contribution of delay to the overall stability of the system. References O. Bernard, Z. Hadj-Sadok, D. Dochain, A. Genovesi, J. P. Steyer. Dynamical model development and parameter identification for an anaerobic wastewater treament process. Biotechnol. Bioeng. 75:424–438, 2001. doi:10.1002/bit.10036 T. F. Thingstad and T. I. Langeland. Dynamics of chemostat culture: The effect of a delay in cell response. J. Theor. Biol. , 48:149–159, 1974. doi:10.1016/0022-5193(74)90186-6 J. R. Beddington and R. M. May. Time delays are not nessarily destabilizing. Math. Biosci. 27:109–119, 1975. doi:10.1016/0025-5564(75)90028-0 K. Y. San and G. Stephanopoulos. The effect of growth rate delays in substrate-inhibited kinetics on the optimal profile of fed-batch reactors. J. Theor. Biol. 28:356–361, 1986. doi:10.1002/bit.260280308 G. Stephanopoulos and K. Y. San. Studies on-line bioreactor identification. I. Theory. Biotechnol. Bioeng. 26:1176–1188, 1984. doi:10.1002/bit.260261006 A. A. Khan, A. J. Stacey and J. J. Shepherd. Optimization of methane output for an anaerobic waste digester. ANZIAM J. 54:C523–C539, 2013. http://journal.austms.org.au/ojs/index.php/ANZIAMJ/article/view/6322 J. F. Andrews. A mathematical model for the continuous culture of microorganisms utilizing inhibitory substrates. Biotechnol. Bioeng. 10:707–723, 1968. doi:10.1002/bit.260100602 D. J. Batstone, J. Keller, I. Angelidaki, S. V. Kalyuzzhni, S. G. Pavlostathis, A. Rozzi, W. T. M. Sanders, H. Siegrist, and V. A. Vavilin. Anaerobic digestion model No. 1 (ADM1). Water Sci. Technol. 45(10):65–73, 2002 http://wst.iwaponline.com/content/45/10/65 K. J. Beers. Numerical methods for chemical engineering: Applications in Matlab . Cambridge, New York, USA, 2007. http://www.cambridge.org/us/academic/subjects/engineering/chemical-engineering/numerical-methods-chemical-engineering-applications-matlab J. F. Andrews. The development of a dynamic model and control strategies for the anaerobic digestion process. In Mathematical Models in Water Pollution Control , A. James (ed). Wiley, 1978. A. W. Bush and A. E. Cook. The effect of time delay and growth rate inhibition in the bacterial treatment of wastewater J. Theor. Biol. 63:385–395, 1976. doi:10.1016/0022-5193(76)90041-2 L. F. Shampine, I. Gladwell and S. Thompson. Solving ODEs with Matlab . Cambridge, New York, USA, 2003. http://www.cambridge.org/us/academic/subjects/mathematics/numerical-analysis/solving-odes-matlab?format=PB

In response to the need for renewable energy resources, the replacement of fuel gas with methane produced from the anaerobic digestion of sewerage, agricultural and municipal solid wastes is considered. The utilization of methane for power generation offsets the energy requirements of the digester facility. We discuss the optimization of methane output for a model digester. The model uses Monod based kinetics of methane fermentation and does not include spatial effects. The model assumes that the solid waste acts as a substrate for acid forming bacteria which produce volatile fatty acids, which is converted to methane by a second type of bacteria. It is found that the initial concentrations of the two bacteria and biodegradable volatile solids that maximize the total methane output are independent of the temperature. However, the optimal hydraulic residence time and initial concentration of volatile fatty acids are temperature dependent. This suggests that flow rates should be adjusted, depending on the temperature, to maximize methane output. References D. T. Hill, Simplified Monod Kinetics of Methane Fermentation of Animal Wastes, Agricultural Wastes, 5:1–16 (1983). doi:10.1016/0141-4607(83)90009-4 D. T. Hill, E. W. Tollner and R. D. Holmberg, The Kinetics of Inhibition in Methane Fermentation of Swine Manure, Agricultural Wastes, 5:105–123 (1983). doi:10.1016/0141-4607(83)90089-6 D. T. Hill, Design Parameters and Operating Characteristics of Animal Waste Anaerobic Digestion Systems–-Swine and Poultry, Agricultural Wastes, 5:157–178 (1983). doi:10.1016/0141-4607(83)90081-1 Y. R. Chen and A. G. Hashimoto, The Kinetics of Methane Fermentation, Biotechnology and Bioengineering Symposium, 8:269–282 (1978). A. Husain, Mathematical Models of the Kinetics of Anaerobic Digestion, Biomass and Bioenergy, 14:561–571 (1998). doi:10.1016/S0961-9534(97)10047-2 D. J. Batstone, J. Keller, I. Angelidaki, S. V. Kalyuzzhni, S. G. Pavlostathis, A. Rozzi, W. T. M. Sanders, H. Siegrist and V. A Vavilin, Anaerobic Digestion Model No. 1 (ADM1), Water Science and Technology, 45:65–73 (2002). http://www.iwaponline.com/wst/04510/wst045100065.htm O. Levenspiel, Chemical Reaction Engineering, 3rd Ed., Wiley, New York (1999). J. F. Andrews, A Mathematical Model for the Continuous Culture of Microorganisms Utilizing Inhibitory Substrates, Biotechnology and Bioengineering, 10:707–723 (1968). doi:10.1002/bit.260100602 K. J. Beers, Numerical Methods for Chemical Engineering: Applications in Matlab, Cambridge, New York, USA (2007).

Anaerobic digestion is one of the most common methods used to generate energy from renewable sources. However, untreated anaerobic liquid digestate may cause eutrophication if directly discharged into the water bodies due to its high nutrient content. Microalgae can assimilate nutrients especially nitrogen and phosphorous from wastewater for their growth and produce valuable biomass. In this study, batch experiments were carried out to investigate the biokinetic coefficients for nutrient removal of mixed microalgae grown on anaerobic liquid digestate by Michaelis–Menten rate expression. The initial NH3-N concentration was varied between 18.6 and 87.1 mg L−1, while initial PO4-P concentration was between 1.85 and 6.88 mg L−1, which corresponds to 2%, 5%, 7%, and 10% dilution ratio of anaerobic digestate. According to the yield results (mg chl a mg−1 nutrient), mixed microalgae uptake 10 times more nitrogen than phosphorus. Biokinetic coefficients were determined as kN = 2.48 mg NH3-N mg−1 chl a day−1, KmN = 29.3 mg L−1, YN = 0.45 mg chl a mg−1 NH3-N for nitrogen; and kP = 0.21 mg PO4-P mg−1 chl a day−1, KmP = 2.94 mg L−1, YP = 5.03 mg chl a mg−1 PO4-P for phosphorus. The highest chlorophyll production (39 mg L−1 or 3.31 mg L−1 day−1) was observed at the highest dilution ratio of 10%. Moreover, the highest dilution resulted in highest biomass (1.25 g L−1) despite of dark, high ammonicial, and particulate rich wastewater.

Synthetic microbial communities (SynComs) are powerful tools for investigating microbial interactions and community assembly by focusing on minimal yet functionally representative members. Here, we will highlight key principles for designing SynComs, specifically emphasizing the anaerobic digestion (AD) microbiome for waste treatment and upcycling. The AD process has traditionally been used to reduce organic waste volume while producing biogas as a renewable energy source. Its microbiome features well-defined trophic layers and metabolic groups. There has been growing interest in repurposing the AD process to produce value-added products and chemical precursors, contributing to sustainable waste management and the goals of a circular economy. Optimizing the AD process requires a better understanding of microbial interactions and the influence of both biotic and abiotic parameters, where SynComs offer great promise. Focusing on AD microbiomes, we review the principles of SynComs' design, including keystone taxa and function, cross-feeding interactions, and metabolic redundancy, as well as how modeling approaches could guide SynComs design. Furthermore, we address practical considerations for working with AD SynComs and examine constructed SynComs designed for anaerobic waste digestion. Finally, we discuss the challenges associated with designing and applying SynComs to enhance our understanding of the AD process. This review aims to explore the use of synthetic communities in studying anaerobic digestion and highlights their potential for developing innovative biotechnological processes.

BackgroundA major problem with farming systems is the deficiencies in phosphorus (P) due to fixation in soils, erosion and run-off, and exports of herbal and animal products. P resources for the compensation of these losses will sooner or later be depleted. For this reason, innovative ideas for phosphorus recycling are highly relevant.The P excess from farming systems mostly ends up in surface waters, leads to eutrophication, and promotes the growth of aquatic plants. Particularly invasive neophytes such as western waterweed (Elodea nuttallii) can rapidly generate high levels of biomass in waters with good nutrient supply and bind relevant amounts of phosphorus.MethodsIn the renatured open-pit mine Goitzsche (Saxony-Anhalt, Germany), biomass from E. nuttallii was harvested (2005–2008) and the biomass dry matter and the P concentration were determined. The phosphorus recovery potential from this plant biomass was calculated by extrapolation based on the phosphorus analyses and the area potentially populated by E. nuttallii. One analysis of E. nuttallii was conducted to evaluate the content of potentially toxic elements (PTEs).ResultsThe results showed that with 0.5 to 6.3 kg P/Mg of total solid (dry matter), E. nuttallii could have a high potential to recycle phosphorus, e.g., by anaerobic digestion and digestate fertilization. Lake Goitzsche offered an annual recovery potential from 0.5 to 1.7 Mg phosphorus in the investigation period. This could meet the needs of 114-ha organic farming land based on a 7 kg/(ha*year) regional phosphorus deficit.The digestate of E. nuttallii is very well suited as a fertilizer due to its high phosphorus concentration. The concentrations of PTEs in the current digestate (related to an individual case) are sufficient for legal admission in Germany. In this study, nickel was above the threshold values for Germany. The elevated nickel levels in the Elodea biomass correspond to the geogenic high nickel concentrations in the sediment of this lake.ConclusionsAquatic macrophytes have a significant potential for recovering phosphorus from waters and sediments of relevant phosphorus concentrations. Further studies of surface water zones, particularly with regard to the aquatic plant biomass and phosphorus concentration of sediments, are needed to assess future exploration.

The use of renewable energy sources including biomass for energy generation, to achieve diversification in energy production, has been found to be sustainable economically, financially and environmentally. Various energy production technologies exist by which biomass can be converted for energy generation. Such technologies include anaerobic digestion, gasification, thermal depolymerization, pyrolysis, fermentation, anaerobic digestion, amongst others. The focus of this study is on the use of anaerobic digestion technology. Anaerobic digestion is recognized as one of the best options for treating biomass as it helps to avoid CO₂ emissions and run off of biomass. It is a natural process in which bacteria convert organic materials into biogas and fertilizer production in an environmentally friendly way. Anaerobic digestion is a series of sequential process including hydrolysis, acidogenesis, acetogenesis and methanogenesis. Different models have been applied to capture the characteristics of the anaerobic digestion process such as first-order model, Gompertz model and logistic model. However, Gompertz model is considered as the best model in describing the growth of animals and plants as well as the volume of bacteria. It is also used to describe the cumulative biogas production curve in batch digestion assuming that substrate levels limit growth in a logarithmic relationship. This study developed a System Dynamics model (SDM) for predicting biogas production (BP) in an anaerobic condition, based on Gompertz-Laird model. The objective is to describe the process of a System Dynamic (SD) model of two stage kinetics of BP. Primary data used were obtained from a laboratory experiment of BP using vegetal wastes, while secondary data were obtained from literature on studies using similar substrates. The Causal loop diagram generated, describes the anaerobic digestion (AD) process usually undergone by a substrate, while the Stock Flow diagram depicts the building blocks of the dynamic behavior of the same process. The developed SD model consists of two-level variables which depict the equations driving the AD process represented as hydrolysis-acidogenesis and acetogenesis-methanogenesis. The model results showed a significant lag phase between methanogenesis and fermentation stage, which was found to be linked to the inoculum-substrate ratio. The study conclusion includes: inoculum to substrate ratio affects BP; inconsistency of the experimental data caused by inhibition explains the variation observed between the empirical and simulated results.

Effectively managing and transforming organic waste into a valuable resource is critical for minimising environmental impact, conserving resources, and mitigating climate change. Anaerobic digestate of solid food waste has high ammonium (NH4+) concentration and discharging it into the environment after nitrification may cause eutrophication. This study aimed to characterise (i) the adsorption of NH4+ from anaerobic digestate of food waste by biochar derived from mixed eucalypt (Eucalyptus spp.) tree species before and after modification with HNO3 and Na2CO3 and (ii) the use of NH4+-loaded biochar as a potential N fertiliser. The isotherm and kinetics experiments using pure NH4+ solution and anaerobic digestate solution revealed that modifications to eucalypt biochar enhanced NH4+ adsorption capacity, predominantly through ion exchange and electrostatic interaction related to cation exchange capacity. A glasshouse pot study using maize plants was conducted with ammonium-loaded pristine and modified eucalypt biochar. The batch sorption data were fitted to Langmuir and Freundlich models for the isotherm and pseudo-first order, pseudo-second order, Elovich, and intraparticle diffusion models for the kinetics. The pseudo-secondorder and Elovich models closely matched the experimental breakthrough curves for NH4+. Post-modification, the eucalypt biochar effectively extracted NH4+ from pure NH4+ solution and digestate, primarily through chemisorption via ion exchange, electrostatic interaction, cationic interaction. A glasshouse pot study using maize plants revealed that ammonium-loaded pristine and modified eucalypt biochar increased plant growth, suggesting that it can be used as an alternative to synthetic N fertiliser. Modified eucalypt biochar might be suitable for treating digestate liquid from various sources and reducing NH4+ concentration and N losses from digestate liquid. Enriched modified biochar might be reused as nitrogen fertiliser in the soil.

Anaerobic digestion (AD) as a waste management strategy for the organic fraction of municipal waste (OFMSW) has received attention in developed countries for several decades, leading to the development of large-scale plants. In contrast, AD of OFMSW has only recently drawn attention in developing countries. This systematic review was carried out to investigate the implementation of AD to treat the OFMSW in developing countries, focusing on assessing pilot and full-scale AD plants reported in the last ten years. Studies that met the selection criteria were analyzed and data regarding operating parameters, feedstock characteristics, and biogas, digestate, and energy production were extracted. As outlined in this systematic review, AD plants located in developing countries are mostly one-stage mesophilic systems that treat OFMSW via mono-digestion, almost exclusively with the aim of producing electrical energy. Based on the analysis done throughout this systematic review, it was noted that there is a large difference in the maturity level of AD systems between developing and developed countries, mainly due to the economic capacity of developed countries to invest in sustainable waste management systems. However, the number of AD plants reported in scientific papers is significantly lower than the number of installed AD systems. Research articles regarding large-scale implementation of AD to treat OFMSW in developed countries were analyzed and compared with developing countries. This comparison identified practices used in plants in developed countries that could be utilized in the large-scale implementation and success of AD in developing countries. These practices include exploiting potential products with high market-values, forming partnerships with local industries to use industrial wastes as co-substrates, and exploring different biological and physical pretreatment technologies. Additionally, the analysis of capital and operational costs of AD plants showed that costs tend to be higher for developing countries due to their need to import of materials and equipment from developed countries. Technical, economical, and political challenges for the implementation of AD at a large-scale in developing countries are highlighted.

Physical-chemical traits, phytotoxicity and pathogen detection in liquid anaerobic digestates

Membrane separation technologies offer a promising solution for anaerobic digestate treatment but are limited by membrane fouling and reduced flux. This study investigated the use of CuO nanoparticles (NPs) on ultrafiltration membranes to mitigate fouling and improve separation performance during digestate treatment. CuO NPs were synthesized via a sonochemical process and deposited onto NADIR® UP150 T membranes. The modified and unmodified membranes were evaluated using anaerobic sludge from a pilot-scale anaerobic digester under two operational modes: continuous and intermittent with reverse flow cleaning. Results showed that although modified membranes had slightly lower initial permeate flow rates, they exhibited greater stability over time and reduced fouling rates compared to the unmodified membrane. Under intermittent cleaning, the unmodified membrane displayed the highest cleaning impact, with a 100% increase in permeate flow post-cleaning, versus 66.7–88.9% for coated samples. The findings suggest that CuO-modified membranes can provide a trade-off between fouling resistance and flux performance, particularly in systems with limited cleaning capacity.

Aim: A Community-Based Anaerobic Digester was designed in this study for sustainable solid waste management in Ile-Oluji, Ondo state Nigeria.
 Methodology: Waste samples were collected from selected households for a period of one month and the components and percentage composition were determined. Afterwards, the physico-chemical characteristics of the substrate was investigated and the result used to design a community-based anaerobic digester.
 Results: The quantity, components and characteristics of waste generated was determined. The rate of waste generation was found to be 0.2kg/capita/day while the organic fraction of the total waste generated was found to be 55.7%. Physico-chemical characterization of the substrate was also investigated. The pH was found to be 6.36 ± 0.18, while the alkalinity 692.81 ± 78.62. The moisture content was found to be in the range of 71.20 ± 4.63%. Total solid was in the range 38.91 ± 5.25 while volatile solid was found to be 26.44 ± 2.83. carbon oxygen demand was found to be 834.33 ± 12.61, total phosphorus was in the range 4.20 ± 0.33. The Carbon on a dry weight basis was found to be in the range 60.41 ± 2.38, while nitrogen was found to be 4.79 ± 1.03. The C/N ration was found to be 21.61. The biogas yield ranged from 0 – 320 cm3 and 0 – 380cm3 per litre of substrate for biodegradable-only samples and biodegradable-cow dung samples respectively, for a forty days period of retention. The cylindrical dome type biogas digester was chosen for this study because of its simplicity in design and maintenance coupled with lower set up cost. The optimum volume of hydraulic chamber and gas storage chamber were designed to be the same as 850m3. Volume of fermentation chamber and sludge layer were calculated to be 2014m3 and 246m3 respectively, while the height and diameter of the fermentation chamber were 7m and 17m respectively.
 Conclusion: Anaerobic digestion of the biodegradable fraction of solid waste is a viable alternative that government and non-government organizations can key into for the improvement of public health especially in developing countries. The standardization of digester design parameters may pose challenges because of varying climatic conditions and complex socio-economic factors across different geographical contexts. Solutions may have to be adapted and localized to achieve a sustainable world.

Inhibitors of sterol biosynthesis and growth in plants and fungi

Benzyl butyl phthalate activates prophage, threatening the stable operation of waste activated sludge anaerobic digestion

Anaerobic digestion of lignocellulosic waste for enhanced methane production and biogas-digestate utilization

Manure and slurry may contain a range of bacterial, viral and parasitic pathogens and land application of these organic fertilisers typically occurs without prior treatment. In-situ treatment through farm-based anaerobic digestion (AD) of such organic fertilisers co-digested with food-production wastes is multi-beneficial due to energy recovery, increased farm incomes and noxious gas reduction. Before risk assessment can be carried out at field scale an investigation of the fate of relevant target pathogens during the actual AD process must be undertaken, requiring the development of practical test systems for evaluation of pathogen survival. The present study examines miniature (50 mL) and laboratory (10 L) scale AD systems. Treatments included slurry co-digested with fats, oils and grease (FOG) under typical operating and pasteurisation conditions used in farm-based AD, in batch-fed miniature and laboratory mesophilic (37°C) continuously stirred tank reactors. Biogas production, pH, chemical oxygen demand, volatile solids and ammonia concentration were measured throughout the trial, as were faecal indicator bacteria (FIB) i.e. total coliforms, Escherichia coli and Enterococcus species. The miniature and laboratory bioreactors performed similarly in terms of physicochemical parameters and FIB die-off. In the absence of pasteurisation, after 28 days, enterococci numbers were below the <1000 cfu g-1 threshold required for land application, while E. coli was no longer detectable in the digestate. For comparison, FIB survival in slurry was examined and after 60 days of storage, none of the FIB tested was <1000 cfu g-1, suggesting that slurry would not be considered safe for land application if FIB thresholds required for AD digestate were to be applied. Taken together we demonstrate that i) miniature-scale bioreactors are valid proxies of farm-based AD to carry out targeted pathogen survival studies and ii) in situ AD treatment of slurry prior to land application reduces the level of FIB, independently of pasteurisation, which in turn might be indicative of a decreased potential pathogen load to the environment and associated public health risks.