Cement, Energy and Environment

system to get the moisture to the surface and picked up by dry air. The humid air inside the greenhouse is exchanged by a ven la on system. Solar drying requires a large space but low electricity demand. In November 2016, a trial of open sun-drying and solar drying (a basic shed with a fan) of sludge was undertaken. The tests lasted for 40 days with 30-45 cm sludge layer thickness and 90% moisture reduc on was achieved. The sludge was mixed every 2 days. Inside the shed, the average temperature was approximately 1 °C higher and 5% be er efficiency was reached. As per the calcula ons, approximately 1 ha area will be required for drying of CETP sludge for 30 days, to reduce moisture content to 10%. Currently, 0.2 ha area is available which means the sludge from decanters can only be dried for 7- 8 days or only 20% of the CETP sludge generated can be solar or open-sun dried. With 4 months of monsoon period, open sun drying may not be possible to carry out. The electrical energy consump on assumed is 30 kWh per ton of evaporated water which correspond to 0.32 MJ per kg at 10% moisture. The solar drying allows to avoid use of light fuel oil (typical fuel used for thermal sludge drying) and therefore a saved energy of 6.5 MJ/kg and 7.48 MJ/kg sludge at 25% and 10% moisture is assumed, respec vely. These assump ons are also used in this study and directly modelled in the landfill and co-processing scenarios when solar drying is used as pre-treatment. The data on emissions to air during solar drying are not available and therefore the impacts could not be evaluated. The expected emissions from solar drying are majorly methane and carbon dioxide and from thermal drying are vola le organic compounds and vola le heavy metals (such as cadmium). Evalua on of emissions from sludge drying is one of the limita ons of the present study and could be taken up in future. Figure 2: Solar drying facility in Palsana CETP, Surat where moisture content of secondary CETP sludge is reduced from 60% to 10% 58