Study of Coal Conditioning Effects on Dewatering of Pulp and Paper Sludges, 1993 Environmental Conference Proceedings

Many industries have recently realized that the use of polymers is not the most effective or efficient means of conditioning all sludge suspensions. Therefore, research on other means of conditioning, such as physical conditioning agents, has resurfaced. This study examined the effects of the addition of pulverized coal to pulp and paper primary sludge under constant-pressure, cake filtration. The range of coal dosages selected was aimed at maintaining combustion of the filter cake in a boiler furnace. The coal addition range was zero to 1.6 grams coal per gram dry sludge solids (0 - 1.6 g/g DSS).

A compression-permeability cell (C-P cell) was used to perform a complete expression process (filtration and consolidation) on each primary sludge suspension examined. Three major filtration and consolidation parameters were used to assess the effectiveness of coal addition on the suspensions: average specific resistance, filter cake moisture content, and filtration yield. Overall, average specific resistance to filtration decreased with increased coal addition up to a dosage of 1.0 g/g DSS. Filtration yield, which accounts for rate changes, increased by a factor of approximately two with increased coal addition compared to unconditioned sludge. This is a significant advantage if time limitations or reduced capital cost are considered. However, on an energy basis increased coal addition was a disadvantage. Cake solids content of the filter cakes on a DSS basis decreased (or moisture content increased) with increasing coal addition. Therefore, more energy is required to combust the additional water in the filter cake.