INFLUENCE OF MICRONUTRIENTS CONCENTRATION ON SLUDGE ANAEROBIC DIGESTION

Abstract

The management of secondary sludge is complicated point by being a costly matter in wastewater treatment plants. Before their final disposal, normally it is treated inside anaerobic reactors to reduce the total amount of biosolids and therefore their management cost. Any improvement of this process with low cost strategies is an important research item to reduce the energy demand and the cost balances in these plants.In the first part of this master thesis the thermoelectric fly ash was used as a source of micronutrients for anaerobic microorganisms. It was found that it was possible to triplicate the methane generation rate in thermal pre-treated (120 ºC) sludge with ash supply; while in case of no addition, the methane generation rate was 1.4 ml/d while with 150 mg of ash per liter this generation changes to 4.48 ml/l. Also the hydrolytic matter degradation kinetic was obtained in both cases using batch reactors; for the case of no addition the first order kinetic parameter was 0.019±0.002d-1, when ashes were added this value was 0.046±0.000 d-1. Therefore, the addition of these compounds is able to improve the methane generation and hydrolytic kinetics together.In the second part of this master thesis how to reduce de sampling time of this assays was studied by combination of advanced statistical methods with the background experiment reported in this assays. These experimental tests are the analytical key techniques to assess the implementation and optimization of anaerobic biotechnologies. This chapter develops a mathematical strategy using sensitivity functions for early prediction of first-order methane generation model parameters. The minimum testing time for early parameter estimation showed a potential correlation with the substrate degradation kinetic constant rate: (i) slowly biodegradable substrates (k = 0.1 d-1) with minimum testing times of at least 15 days, (ii) moderately biodegradable substrates (0.1 <k< 0.2 d-1) with minimum testing times between 8 and 15 days, and (iii) rapidly biodegradable substrates (k = 0.2 d-1) with testing times lower than 7 days.