J. Mata-Alvarez

Anaerobic digestion of organic solid wastes. An overview of research achievements and perspectives

The technology of anaerobic digestion of organic solid wastes is, in many aspects, mature. Topics such as fundamentals (kinetics, modelling, etc.), process aspects (performance, two- and single-phase systems, wet and dry technologies), digestion enhancement (several pre-treatments), co-digestion with other substrates and its relation to composting technology are examined in this review. Special attention is paid to the advantages of anaerobic digestion in limiting the emission of greenhouse gases. An overview of industrial achievements and future developments is given.

Biomethanization of the organic fraction of municipal solid wastes

1.Fundamentals of the anaerobic digestion process 2.Reactor sizing, process kinetics, and modelling of anaerobic digestionof complex waste 3.Analysis and optimisation of the anaerobic digestion of the organicfraction of municipal solid waste 4.Anaerobic digestion of the organic fraction of municipal solid waste:a perspective 5.Types of anaerobic digester for solid wastes 6.Characteristics of the OFMSW and behaviour of the anaerobic digestionprocess 7.Co-digestion of the organic fraction of municipal waste with otherwaste types 8.Pretreatments for the enhancement of anaerobic digestion of solidwastes 9.Use of hydrolysis products of the OFMSW for biological nutrientremoval in wastewater treatment plants 10.Products, impacts and economy of anaerobic digestion of OFMSW 11.Anaerobic digestion of organic solid waste in bioreactor landfills

Nitrification, denitrification and biological phosphorus removal in piggery wastewater using a sequencing batch reactor

Nutrients in piggery wastewater with high organic matter, nitrogen (N) and phosphorus (P) content were biologically removed in a sequencing batch reactor (SBR) with anaerobic, aerobic and anoxic stages. The SBR was operated with 3 cycles/day, temperature 30 degrees C, sludge retention time (SRT) 1 day and hydraulic retention time (HRT) 11 days. With a wastewater containing 1500 mg/l ammonium and 144 mg/l phosphate, a removal efficiency of 99.7% for nitrogen and 97.3% for phosphate was obtained. Experiments set up to evaluate the effect of temperature on the process showed that it should be run at temperatures higher than 16 degrees C to obtain good removals (> 95%). Batch tests (ammonia utilization rate, nitrogen utilization rate and oxygen utilization rate) proved to be good tools to evaluate heterotrophic and autotrophic biomass activity. The SBR proved to be a very flexible tool, and was particularly suitable for the treatment of piggery wastewater, characterized by high nutrient content and by frequent changes in composition and therefore affecting process conditions.

Codigestion of solid wastes: a review of its uses and perspectives including modeling.

The last two years have witnessed a dramatic increase in the number of papers published on the subject of codigestion, highlighting the relevance of this topic within anaerobic digestion research. Consequently, it seems appropriate to undertake a review of codigestion practices starting from the late 1970s, when the first papers related to this concept were published, and continuing to the present day, demonstrating the exponential growth in the interest shown in this approach in recent years. Following a general analysis of the situation, state-of-the-art codigestion is described, focusing on the two most important areas as regards publication: codigestion involving sewage sludge and the organic fraction of municipal solid waste (including a review of the secondary advantages for wastewater treatment plant related to biological nutrient removal), and codigestion in the agricultural sector, that is, including agricultural – farm wastes, and energy crops. Within these areas, a large number of oversized digesters appear which can be used to codigest other substrates, resulting in economic and environmental advantages. Although the situation may be changing, there is still a need for good examples on an industrial scale, particularly with regard to wastewater treatment plants, in order to extend this beneficial practice. In the last section, a detailed analysis of papers addressing the important aspect of modelisation is included. This analysis includes the first codigestion models to be developed as well as recent applications of the standardised anaerobic digestion model ADM1 to codigestion. (This review includes studies ranging from laboratory to industrial scale.)

Anaerobic co-digestion of pig manure and crude glycerol at mesophilic conditions: Biogas and digestate

Crude glycerol derived from biodiesel production is characterized by its high concentration of organic carbon and its solubility in water; properties that make it a suitable co-substrate to improve the efficiency of a manure digester. An increase of about 400% in biogas production was obtained under mesophilic conditions when pig manure was co-digested with 4% of glycerol, on a wet-basis, compared to mono-digestion. The increase in biogas production was mainly a consequence of the increase in organic loading rate. However, the differences could also be related to the synergy between both substrates and the carbon-to-nitrogen ratio. Moreover, the analysis of the macro-compounds, protein, lipids, carbohydrates and fibers, showed lower removal efficiencies in the co-digester as the microorganisms obtained nutrients from the soluble carbohydrates provided by the glycerol. The digestate stability, evaluated through a respirometric assay, showed that co-substrate addition does not exert a negative impact on digestate quality.

Anaerobic digestion of the Barcelona central food market organic wastes: Experimental study

Abstract Experiments carried out to obtain data for a preliminary design of an anaerobic digestion plant treating the organic wastes coming from a large food market are described. Four hydraulic retention times (8, 12, 14 and 20 days) were tested in 3-litre laboratory digesters. The methane yields were high (around 0·478 m3 CH4/kg VS added). Kinetic analysis, using a first-order model, resulted in a kinetic constant of 3·1 day−1 and an ultimate methane yield of 0·489 CH4/kg VS added. The biogeradability of the soluble and non-soluble fractions of the Volatile Solids (VS) is discussed.

Modified version of ADM1 model for agro-waste application

Agro-residues account for a large proportion of the wastes generated around the world. There is thus a need for a model to simulate the anaerobic digestion processes used in their treatment. We have developed model based on ADM1, to be applied to agro-wastes. We examined and tested the biodegradability of apple, pear, orange, rape, sunflower, pig manure and glycerol wastes to be used as the basis for feeding the model. Moreover, the fractions of particulate COD (X(c)) were calculated, and the disintegration constant was obtained from biodegradability profiles, considering disintegration to be the limiting process. The other kinetic and stoichiometric parameters were taken from the ADM1 model. The model operating under mono-substrate and co-substrate conditions was then validated with batch tests. At the same time the model was validated on a continuous anaerobic reactor operating with pig manure at lab scale. In both cases the correlation between the model and the experimental results was satisfactory. We conclude that the anaerobic digestion model is a reliable tool for the design and operation of plants in which agro-wastes are treated.

Municipal Solid Waste

Municipal solid waste production has increased over the past years. The European Union Waste Framework Directive establishes different hierarchy levels for its management, where prevention and recycling appear as the most convenient management strategies for the organic fraction of MSW. This fraction can be either recycled by composting or by anaerobic digestion followed or not by composting. Anaerobic digestion has the advantage of producing energy instead of consuming it and it is widely described in this chapter. First, a revision of the state of the art of its implementation at full scale is carried out. Then, a detailed description of the environmental and operational factors affecting the process performance is described. Finally, methods for improving the yields of the anaerobic digestion process are considered, which includes biological and physical pre-treatment technologies together with the basis and possibilities of anaerobic co-digestion.

Co-digestion of pig manure and glycerine: Experimental and modelling study

It is a fact that the rapid increase of biodiesel production over the last years has resulted in the generation of large and constant amounts of glycerine, which is causing an oversupply problem. Since glycerine is a biodegradable organic compound exempt of nitrogen, it can be applied as a co-substrate in the anaerobic digestion process of pig manure (PM). In order to analyze the feasibility of a mixture of pig manure and glycerine in anaerobic processes and to define the effect originated by the nitrogen limitation when large amounts of glycerine are added, several biodegradability batch tests were performed with different mixtures. These were named as: 100% PM, 80% PM, 60% PM, 40% PM and 20% PM, in pig manure wet weight-basis. Furthermore, a modified model based on anaerobic digestion model no.1 (ADM1) was used to simulate the methane production profiles for the mixtures tested. Specifically, both experimental and model results show the power of the co-digestion technology. In particular, the mixture of 80% PM produced the highest methane production with 215 mL CH(4) g(-1) COD, almost 125% more methane than when pig manure was mono-digested. In contrast, the one with 20% PM was clearly inhibited by the volatile fatty acid due to the low nitrogen concentration of the mixture. In addition, the specific methane production predicted by the model was in good agreement with the experimental results, although in some samples the shape of the profiles did not match perfectly. Moreover, the modified ADM1 appears to be a useful tool to predict the methane production and the limitations related to the lack/excess of nitrogen during the co-digestion process of pig manure and glycerine.

Ammonia influence in anaerobic digestion of OFMSW

The anaerobic digestion of the organic fraction of municipal solid wastes is taking increasing importance in the recent years. The main problem of some anaerobic digestion process is the large quantity of ammonia that is released, especially when high solid digestion is implemented. A fraction of the supernatant is treated and the remaining is recirculated to maintain the reactor in the optimum solids concentration. The question arising is if this recirculation stream should also be treated to improve biogas production. However, when doing the latter the quantity of ammonia inside the reactor increases too which could lead to inhibit the reactor operation. In this paper it appears that not only free ammonia affects the methanogenic fermentation but also ammonium ion concentration. Biogas production profiles are estimated using the Gompertz model. On the other hand, inhibition constants are fitted using a non-competitive inhibition model equation Thus, 50% inhibition of biomethane production was observed at level of 215 and 468 mg NH3_N/L under mesophilic and thermophilic conditions. However, the methane generation under mesophilic and thermophilic conditions was reduced by 50% when ammonium ion reach concentrations of 3,860 and 5,600 mg NH4+_N/L respectively. Under mesophilic conditions, pH higher than 7 impacted the methanogens bacteria negatively. This threshold pH limit, is variable under thermophilic conditions, depending on the total ammonia concentration.