Wastewater generated during cleaning/washing procedures in a wood-floor industry: toxicity on the microalgae Desmodesmus subspicatus.

In industries based on dry processes, such as wood floor and wood furniture manufacture, wastewater is mainly generated after cleaning of surfaces, storage tanks and machinery. Owing to the small volumes, onsite treatment options and potential environmental risks posed to aquatic ecosystems due to discharge of these wastewaters are seldom investigated. In the present study, the effects of cleaning wastewater streams generated at two wood floor production lines on Desmodesmus subspicatus were investigated. The microalgae was exposed to different wastewater concentrations (100, 50, 25, 12.5 and 6.25% v:v) and the algae growth evaluation was based on in vivo chlorophyll fluorescence, cell density, cell size (number of cells/colony) and cell ratio (length/width). Inhibitory effects of the tested wastewaters on the microalgae were positively related to concentration and negatively related to exposure time. The EC50,24 h of blade cleaning wastewater (BCW) and floor cleaning wastewater (FCW) were 3.36 and 5.87% (v:v), respectively. No negative effect on cell colony formation was caused by BCW, whereas an increase of 90% unicellular cells was observed in FCW concentrations below 50% (v:v). At the lowest concentration (3.13% v:v) where no growth inhibition was observed, both wastewater streams caused changes in cell dimensions by increasing cell length and width. To conclude, wastewaters generated during cleaning procedures in the wood floor industries can have severe environmental impacts on aquatic organisms, even after high dilution. Therefore, these wastewaters must be treated before being discharged into water bodies.