GISCOD: general integrated solid waste co-digestion model.

This paper views waste as a resource and anaerobic digestion (AD) as an established biological process for waste treatment, methane production and energy generation. A powerful simulation tool was developed for the optimization and the assessment of co-digestion of any combination of solid waste streams. Optimization was aimed to determine the optimal ratio between different waste streams and hydraulic retention time by changing the digester feed rates to maximize the biogas production rate. Different model nodes based on the ADM1 were integrated and implemented on the Matlab-Simulink simulation platform. Transformer model nodes were developed to generate detailed input for ADM1, estimating the particulate waste fractions of carbohydrates, proteins, lipids and inerts. Hydrolysis nodes were modeled separately for each waste stream. The fluxes from the hydrolysis nodes were combined and generated a detailed input vector to the ADM1. The integrated model was applied to a co-digestion case study of diluted dairy manure and kitchen wastes. The integrated model demonstrated reliable results in terms of calibration and optimization of this case study. The hydrolysis kinetics were calibrated for each waste fraction, and led to accurate simulation results of the process and prediction of the biogas production. The optimization simulated 200,000 days of virtual experimental time in 8 h and determined the feedstock ratio and retention time to set the digester operation for maximum biogas production rate.

Evaluation of a new fixed-bed digester design utilizing large media for flush dairy manure treatment.

A new anaerobic digester design for the treatment of diluted (<2% solids) flush dairy manure was evaluated. The new design was developed as an economic alternative for enhancing the performance of anaerobic lagoon systems in cold weather areas. The digester employed used automobile tires as fixed-bed media to improve bacterial retention. The digester was heated by steam injection and built underground to enhance insulation. The tires were sorted in a unique pattern for improving mixing and uniform temperature distribution. The system was tested on a pilot-scale. The treatment mechanism was explored by mathematical modeling. The observed treatment efficiency of the new design was comparable to that of conventional digesters operating at higher total solids concentrations (>4%). With a hydraulic retention time (HRT) of 17 days, the measured removal rates were 30-50% and 40-60% of TVS and COD, respectively. The new digester maintained longer solids retention time (SRT) as estimated using the model, supported by the observed thick biofilm formation and resistance to hydraulic overload. The model was used to analyze different operation scenarios varying both the organic and hydraulic loads.

Automatic initialisation of buffer composition estimation for on-line analysis of unknown buffer solutions.

An automatic initialisation procedure for extracting useful information about buffer composition from a titration experiment is presented in this paper. The initialisation procedure identifies which buffering components are present in the sample from a relatively long list of buffers expected in the system monitored. The procedure determines approximate pKa values of the buffers and evaluates their maximum and minimum concentrations. This information is then used to start an optimisation procedure to fit the model of the buffer components to the titration data and to accurately determine buffer concentrations and pKa values. The procedure has been integrated as a software layer around the buffer capacity optimum model builder (BOMB) that fits a buffer-capacity model to a measured buffer-capacity curve to estimate model properties (pKa values and concentrations). The reliability and robustness of the resulting buffer capacity software (BCS) were tested using a titrimetric analyser simulator (TAS). The BCS was then validated off-line and on-line.