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To optimize the anaerobic digestion process of residual sludge, co-substrates addition and pre-treatments are increasingly being employed. Nevertheless, if these processes allow the optimization of biogas production, they can significantly impact the efficiency of mechanical dewatering processes for digested sludge. In this article, the impact of co-substrate addition (oily sludge) and thermal pre-treatment on the efficiency of mechanical dewatering of digested sludge was investigated. To this purpose, mechanical dewatering experiments were conducted at lab-scale by using a filtration-compression cell to determine the limit dryness of various digestates. In addition, control factors of the mechanical dewatering efficiency of digested sludge were investigated. Results highlight that 67% of the variance of the limit dryness of digestates is due to the variable “volatile solid/total solid ratio.” [ABSTRACT FROM AUTHOR]

Abstract: In this study, a procedure accounting for degradation kinetics was developed to split the total COD of a substrate into each input state variable required for Anaerobic Digestion Model n°1. The procedure is based on the combination of batch experimental degradation tests (“anaerobic respirometry”) and numerical interpretation of the results obtained (optimisation of the ADM1 input state variable set). The effects of the main operating parameters, such as the substrate to inoculum ratio in batch experiments and the origin of the inoculum, were investigated. Combined with biochemical fractionation of the total COD of substrates, this method enabled determination of an ADM1-consistent input state variable set for each substrate with affordable identifiability. The substrate to inoculum ratio in the batch experiments and the origin of the inoculum influenced input state variables. However, based on results modelled for a CSTR fed with the substrate concerned, these effects were not significant. Indeed, if the optimal ranges of these operational parameters are respected, uncertainty in COD fractionation is mainly limited to temporal variability of the properties of the substrates. As the method is based on kinetics and is easy to implement for a wide range of substrates, it is a very promising way to numerically predict the effect of design parameters on the efficiency of an anaerobic CSTR. This method thus promotes the use of modelling for the design and optimisation of anaerobic processes. [Copyright &y& Elsevier]

Abstract: In this study, the maximum ratio of greasy sludge to incorporate with waste activated sludge was investigated in batch and CSTR experiments. In batch experiments, inhibition occurred with a greasy sludge ratio of more than 20–30% of the feed COD. In CSTR experiments, the optimal greasy sludge ratio was 60% of the feed COD and inhibition occurred above a ratio of 80%. Hence, batch experiments can predict the CSTR yield when the degradation phenomenon are additive but cannot be used to determine the maximum ratio to be used in a CSTR configuration. Additionally, when the ratio of greasy sludge increased from 0% to 60% of the feed COD, CSTR methane production increased by more than 60%. When the greasy sludge ratio increased from 60% to 90% of the feed COD, the reactor yield decreased by 75%. [Copyright &y& Elsevier]