Mary-Ann Ochota visits Bangladesh and India to ask why 2.3bn people lack adequate toilets.
Sybil Ruscoe is at a farm growing maize to produce electricity by anaerobic digestion.
Alice Roberts discovers the potential savings available by harnessing the power of sewage.
Brett Westwood reflects on wildlife changes in his local patch over 40 years.
An investigation into the use of sewage sludge as fertiliser on agricultural land.
Raw sewage regularly pours into the River Thames. Alice Roberts looks for an answer.