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.