Rice Husks

The production of rice husks is about 100 million tons per year. Only a fraction of it is used as animal bedding or as fuel for energy production. In Asia bri­quettes are produced from rice husks. These are expen­sive to produce, due to the silicon content of the husks. Hill et al. (1981) obtained 110 l/kg VS at a retention time of 17 days. Pretreatment with 8% NaOH gave a methane yield of 200 l/kg VS (Vevekanandan et al.,

2011) .

Bagasse

Bagasse is the pressed stalks from sugarcane. It is washed to remove nearly all the sugar in the stalks and leaves the factory at 50% humidity with 5% sugar remaining. World production is 140 million tons (dry weight). Most of the bagasse is used as fuel in the sugar

factory and some is made into paper and fiberboard. The factories have an excess of bagasse and this is stored in the open air. The stacks produce methane and open fires are common giving off soot and polluting the air. Bagasse has a low biodegradability of 120 l/kg VS (Table 13.8).

Coffee Husks and Mucilage

The production of coffee husks and mucilage is 5 million tons per year. They are dumped near the fac­tories causing methane emissions and degrading the environment. They have a high lignin content of 21%