Assessment of two-stage anaerobic digestion of blackwater and kitchen waste for reducing environmental impact of residential buildings

Abstract

In recent years, much attention has been directed towards municipal waste management since these residues has become a global challenge with increasing public health, environmental, social, and economic costs. Therefore, there is an urgent need to adopt widely accepted sustainable alternatives and circular economy approaches. In that sense, the decentralized waste management approach has become a feasible and sustainable strategy to valorise and minimize wastes at source. Among the available technologies, anaerobic digestion is widely used as it allows to recover energy in form of biogas from organic waste. This study proposes a decentralized system based on a two-stage anaerobic digestion for the joint valorisation of organic wastes -blackwater and kitchen wastes-in residential buildings. In the first stage (dark fermentation), different ratios of blackwater:kitchen waste were assessed and a maximum volatile fatty acids production of 5000–7000 mg L-1 was reached when 5 kg of black water and 0.30 kg of kitchen waste were added to the system. Then, during second stage, the volatile fatty acids rich stream was valorised in an upflow anaerobic sludge blanket reactor resulting in a biogas production of 5.45 ± 1.34 L d-1, containing 75.6 ± 7.3% of methane and 22.8 ± 5.7% of carbon dioxide while reporting a low content of impurities - 0.02% of hydrogen sulphide and 0.002% of hydrogen -.