Home Running Small-scale

Pre-processing


The feed materials for biogas systems are composed of different biomass materials. Some materials, such as starches and sugars digest very easily. Other, such as woody materials, that contain a large amount of lignin, take a long time to break down. The pre-processing of biogas feed materials can be used to begin the process of breakdown, while separating the materials that are easily digested from those that are not.



Bioplex Nisargruna1

The Nisargruna process, developed by Bhabha Atomic Research Centre (BARC) in Mumbai, India, uses a solar heated aerobic first stage. This accelerates the break down of the food waste that is added to the system, allowing the second stage, which is a standard mesophyllic (35°C) digester generating biogas to process the feed more quickly and efficiently.

Nisargruna plant at BARC, Mumbai

In the UK, Bioplex Ltd developed a thermophyllic (57°C) first stage to separate cattle dung from straw. It can be used to separate digestible matter in food wastes from ligninaceous materials.

The solid materials can be composted and the digestible liquor used in a digester to make biogas.

Nisargruna2

Nisargruna plant, Shatabdi Hospital Site at Govandi, Mumbai

Biotech Ltd in Kerala have a system for processing food waste. Liquor from the main digester is recycled through predigester tanks. Digestible matter is hydrolysed, dissolved and transferred to the main digester. The fibrous material left behind is removed when the level of fibres in the predigester tank is too high.

The World Bank are keen to fund the installation of food waste digestion systems in places such as Nepal. There is a need to develop similar low-cost systems that work on a larger scale than those in Kerala.