Andrew White says he's solved the problem of biogas production creating toxic hydrogen sulfide. The Toronto chemical engineer is turning the sulfide into fertiliser. Biogas has been called a clean, carbon-neutral alternative to fossil fuels. But the decomposition process is dirty. White says his SulfaCHAR pellets are the only product to avoid toxic waste disposal, and the most profitable. It can be used in large farms, landfills, and wastewater treatment plants. His prototype should produce a tonne of fertiliser daily by next Spring. Twelve months on and that figure could be ten tonnes, something White says will help renewable gas plants world-wide turn a profit.