Assessment of solar drying of Brazilian pulp mill primary sludge

Abstract

Pulp mill sludge is a challenging by-product in wastewater treatment plants (WWTP), due to high moisture content, and poor dewatering characteristics. Solar drying was identified as an appropriate pre-treatment to reduce sludge moisture and enhance its energy efficiency for combustion purposes. Brazil is the world’s second-largest pulp producer, and its high intensity of annual solar irradiation makes it a prime candidate for the application of solar sludge drying technology. This study evaluates the main characteristics of primary sludge (PS) from pulp mills at 65% and 95% moisture content. An active passive solar dryer, followed by ASPEN Plus software simulation was used to evaluate drying properties and combustion potential. CO2 emission impact was explored, and the environmental effects of primary sludge combustion after solar drying were estimated. As indicated by the findings, the sludge commenced with a solids concentration of 21%, eventually reaching 95.5%, thereby enhancing its suitability for combustion. From the simulation, a heat rate expenditure in sludge combustion reported 24672 kW and 16295 kW for a solids content of 65% and 95%, respectively. Therefore, employing solar drying before the sludge incineration is crucial for minimizing energy consumption during combustion. Additionally, solar energy being cost-free, offers an opportunity to alleviate environmental harm.