Influence of coal powder and ferric chloride on the dewatering and drying process of sludge at the WWTP of Garmerwolde

The WWTP of Garmerwolde treats the waste water produced by the citizens of Groningen. When cleaning polluted water, sludge is produced as a byproduct. In Garmerwolde the sludge is dewatered by a chamber filter press and the resulting sludge cake with a dry solid content of 22.5% is dried by Swiss Combi with the use of natural gas. The resulting granulates are sold to several other companies to be used as fuel. The cost of sludge cake handling is very expensive and makes the price of drinking water higher. Garmerwolde wants to lower the sludge cake handling cost by the following things: - By using coal powder in the dewatering process. This will create a sludge cake with a higher dry solid content (around 40%) and therefore Swiss Combi has to remove less water. - It is suggested that ferric chloride isn’t needed anymore when using coal powder. Not using any ferric chloride in the process will reduce the sludge cake handling costs. - Swiss Combi uses an expensive way of drying the sludge cake by using natural gas. What is the effect on the drying process if coal powder and ferric chloride are used? In this report the objective is to see whether the above things were indeed a way to improve the dewater ability of the sludge cake and if the sludge cake could be dried by using normal air. The methods used are lab scale experiments to study the effect of coal powder and ferric chloride on the dry solid content of the sludge. The produced sludge cake was then used to obtain sorption isotherms. By measuring sorption isotherms we could see what the effect of different additives (ferric chloride and coal powder) was on the drying process of the sludge cake. The results of the experiments within this research show that adding coal powder has an positive effect on the dewatering process. Dry solid contents of 40% weren’t reached only when using undigested sludge. It was also shown that ferric chloride isn’t needed anymore when using coal powder. In the currently setup used at Garmerwolde, a combination of coal powder and ferric chloride gives the best dewatering results. Lastly it was shown by the sorption isotherm experiments the different additives (coal powder and ferric chloride) didn’t affect the drying process of sludge. A higher mass of water per mass of dry sludge is removed, which results in a higher dry solid content of the sludge. Since less water has to been evaporated in the drying process, this positively effects the reduction in costs.