Impact of zero-discharge implementation on wet-end retention at recycled fiber board mills

One critical issue encountered when implementing zero-discharge operation, is the change in wet-end chemistry due to the build-up of dissolved solids and an increase in headbox temperature. The wet-end chemical program must therefore be followed carefully and modified as zero-discharge is implemented. This is particularly important at recycled fiber board mills because dissolved solids are not typically removed in water treatment before the effluent is recycled to process. The objective of this experimental work was to quantify the impact of zero-discharge implementation on the performance of wet end retention aid programs at a recycled fibre paperboard mill. The performance of retention aid programs was compared for an open mill and a zero-discharge mill. Then, the efficiency of single, dual and microparticle retention aid programs was tested under zero-discharge conditions to compare their relative performance at different dosage levels. Britt Jar experiments were performed to establish changes in retention aid efficiencies. Results showed that zero discharge implementation has a detrimental impact on the efficiency of the wet end retention aid program. More complex polymer programs such as the microparticle program reach better efficiencies under zero-discharge operation, and can be used to maintain acceptable performance of the wet end chemical program while an ''effluent-free'' operation is achieved.