The effect of low hydrolyzed polyvinyl alcohol on the unadapted biocenosis of activated sludge

The field of application of water-soluble films in the food industry includes protective shells of food products, including indicator packaging, water-soluble labels, eco-bags for storing dry and frozen products, etc. The main raw material for the production of water–soluble films is polyvinyl alcohol (PVA), which is used in the food industry as an additive E1203 – emulsifier, moisture retention, glazing agent. Currently, the issue of the effect of PVA on the biocenosis of activated sludge (AS) of wastewater treatment plants, in which water-soluble packaging usually ends its life cycle, has not been sufficiently studied. The purpose of the work is to assess the effect of low-hydrolyzed polyvinyl alcohol on the indicators of unadapted activated sludge of wastewater treatment plants. The object of the study was selected PVA grade 17-88 in the form of a 5% solution, which was introduced in a certain amount into an aqueous-silt mixture (ASM) under laboratory conditions of aerotanks (0.1 and 0.05 wt.%). AS was taken from the well of the secondary settling tank of urban wastewater treatment plants. To assess the effect of PVA on the biocenosis of AS, hydrochemical (GC) and hydrobiological (GB) indicators of sludge, as well as the indicator of chemical oxygen consumption of ASM, were determined in dynamics. It was found that the introduction of PVA into an aqueous-silt mixture at concentrations of 0.1 – 0.05 wt.% has a positive effect on GC and GB indicators of unadapted activated sludge, compared with starving ASM, which was not injected with PVA, having a flocculating effect and contributing to the improvement of sedimentation properties of AS, as well as the preservation of species diversity due to the content of nutrients. It was found that the threshold concentration of PVA content in the aqueous-silt mixture is 0.15 wt.% (which corresponds to chemical oxygen consumption values of about 2500 mgO2/l)), more concentrated solutions due to high foaming and high chemical oxygen consumption values contribute to the removal of biomass and deterioration of GC and GB AS indicators. It was found that on the first day of interaction of PVA and AS, about 20-30% of the polymer mass is withdrawn from the ASM (presumably due to sorption on the extracellular matrix of AS), which is confirmed by a decrease in the value of chemical oxygen consumption, and further stabilization of the chemical oxygen consumption value of the studied systems is observed up to 7 days of the experiment.