Optimization of cow manure and sewage sludge CO-Digestion using disintegration technologies

The environmental problem of manure management and the decreasing availability of land for its disposal are forcingthe development of new waste management strategies. Anaerobic digestion is an attractive treatment for cow manure,since it produces biogas, and a stabilized digestate that can be reused as organic fertilizer (Neves et al., 2008). Codigestion of animal manure with sewage sludge offers economic and environmental benefits due to cost-sharing byprocessing multiple waste streams with complementary characteristics in order to improve the methane production andprevent inhibition problems due to ammonia toxicity.

Further Author:
A. Nielfa - University of Valladolid

In this study, several pretreatment technologies such as thermalhydrolysis (Valo et al., 2004), enzymatic hydrolysis and ultrasounds, have been selected to compare them and optimizethe anaerobic co-digestion of cow manure from slaughterhouse and sewage sludge by the most effective pretreatment. Cow manure was treated with different disintegration technologies in order to compare the effects between them. Then,a mixture of thickened primary and biological sludge sampled from a municipal WWTP was mixed with cow manureaccording to a ratio previously defined (25% COD of the final mixture belongs to cow manure). This ratio was selectedas optimum after carrying out different Biological Methane Potential (BMP) tests to three different ratios (15, 25, 50%COD). The three different disintegration technologies were also applied to the selected mixtures in order to optimize theco-digestion process, looking also for the best configuration. For the analysis control Standard Methods were used andBMP tests were carried out following a previously developed protocol (Angelidaki et al., 2009). Furthermore, otherphysical parameters were characterized in order to assess the implementation of co-digestion mixtures andpretreatments in a continuous operation (filterability, centrifugability and rheology).In a first phase the influence of the three pretreatments in raw cow manure was compared by BMP tests. Ultrasound wasthe only one that increased the methane production of raw substrate, improving it by 19%. Moreover, a higher methaneproduction during the first days was observed for ultrasounds and thermal hydrolysis in comparison to raw substrate,what reflects that the hydrolysis rate is improved by these pretreatments. Then, each pretreatment was applied to themixture of cow manure with primary and secondary sludge. It was observed that the methane productivity increased byall pretreatments, reaching similar values close to 500 mLCH4/gVSadded. The effect of pretreatments was also noticed inthe first days of productivity, observing a quick start-up of the production during the first five days, reaching the 75% ofthe final production. Although Ultra sounds have the highest value for methane potential, thermal hydrolysis presentssome operational and economic advantages (energy integration capacity, continuous implementation) to be selected for a further cow manure co-digestion study. In accordance with previous results, thermal hydrolysis was optimized by theevaluation of three configurations: hydrolyzed cow manure, hydrolyzed secondary sludge or hydrolyzed mixture of cowmanure and secondary sludge. Hydrolyzed samples present for all configurations a higher methane potential than theraw mixture (288 mLCH4/gVSadded). The highest increase (>30%) is obtained for the configurations on which hydrolysisis applied to secondary sludge alone and to the mixture of secondary sludge with cow manure. Other tests focused in theassessment of physical properties showed that thermal hydrolysis improves considerably the hydrodynamic properties of the samples, especially filtration and viscosity. While pretreatments to raw cow manure have not shown improvements on biomethane potential (except forultrasounds), co-digestion increases the production of biogas due to the complementary effect of the substrate andsludge, which is improved by the action of all pretreatments. Thermal hydrolysis advantages convert this pretreatmentin the best option for a further optimization in which the next configurations, hydrolyzed mixture and hydrolyzed secondary sludge, have shown the best results for cow manure and mixed sludge co-digestion.



Copyright: © European Compost Network ECN e.V.
Quelle: Orbit 2012 (Juni 2012)
Seiten: 8
Preis inkl. MwSt.: € 8,00
Autor: Raúl Cano
Maria Fdz-Polanco
Ana Pérez
Lynne Bouchy

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