Optimum anaerobic digestion loading rates
Winter, P.1, Rus Perez, E.2 and Smith, S.R.2, 1Thames Water, UK, 2Imperial College London, UK
(free)
Solids loading rate is a basic operational control parameter for sludge anaerobic digestion (AD) systems, yet the quantitative effects of loading rate on the dynamics, efficiency and stability of the AD process are poorly understood. The aim of this study was to determine the effects of different sludge loading rates on the performance of conventional mesophilic AD.
Controlled experiments were performed using an automated laboratory digester to measure the effects of different loading rate conditions on net gas production. The effects of under loading as well as overloading on the net performance of the AD process were considered. The results showed that the process stability was maintained at organic loading rates of 1.5, 2, and 2.5 kg VS/m3/d. Specific gas production increased in linear response to organic loading rate and improved on average by 17 % from 453 m3/t VS at the lowest feed rate equivalent to 1.5 kg VS/m3/d to 529 m3/t VS at the highest feed rate equivalent to 2.5 kg VS/m3/d. A wider range of organic loading rates was assessed using batch digestion.
Introduction
Anaerobic digestion (AD) is one of the most well-established and cost-effective methods for sewage sludge treatment. Renewable energy generation, rising energy prices, increasing production of sludge, due to population pressure, and tighter requirements for its recycling to agriculture are important challenges for the wastewater industry. Therefore, improving the efficiency of Water Utility assets for sewage sludge treatment, and AD in particular, is critical to maximise resource recovery and sludge recycling. Solids loading rate is a basic operational control parameter for sludge AD systems, yet the quantitative effects of loading rate on the dynamics, efficiency and stability of the AD process are poorly understood. This project explores the impact of organic loading rate (OLR) on biogas production efficiency and stability of the AD process to determine the optimum OLR to maximise gas production.
Keywords: Anaerobic digestion, organic loading, biogas.
