Treatment of wastewater in hybrid constructed wetland from the production of vinegar and packaging of detergents

The results are presented of a 2-year monitoring of the performance of a hybrid constructed wetland (CW), which was created for the treatment of very heterogeneous industrial wastewater (WW) in Slovenia. WW originated from the food-processing department responsible for the production of wine and apple vinegar and from the chemical department in which the packing of detergents and soaps takes place. The hydraulic variability of the WW was high due to the variable production intensity. Low degradability was found due to the remains of detergents in WW. The average efficiency for COD, BOD5, TOC, total organic N, nitrate-N, phosphate and anionic tensides removal was 67%, 66%, 64%, 83%, 83%, 62% and 67%, respectively. Special attention was given to the anionic tensides. Biodegradability and toxicity tests showed the worst results in samples with the highest concentrations of anionic tensides. During intensive vinegar production, the pH of WW was low. In spite of the compensation lagoon, the neutralisation of pH before the inflow into the CW was not always achieved. This presumably caused leaching of Fe from the substratum in the first beds of the CW and its precipitation into the last bed. The CW proved to have a higher pH buffering capacity compared to the open lagoon. In general, the CW verified the predicted results in the first 2 years of its operation. A further increase in efficiency can be achieved via the separate containment of WW with high concentrations of anionic tensides requiring longer degradation period and via the additional buffering of acid outflow from the vinegar production.

The CW showed the predicted results in the first 2 years of its operation. The results demonstrated the limitations of the treatment system due to the influence of WW loadings and its characteristics, and due to the operation conditions of the treatment system. The efficiency of ˇic anionic tensides removal was above 67% despite their poor biodegradability. A further increase in CW efficiency could be achieved via the separate containment of the WW with high concentrations of anionic tensides, which require a longer degradation period, and via the additional buffering of acidic outflow from the vinegar production before inflow into the CW treatment beds. This would also reduce increased Fe concentrations at the outflow and clogging of the beds due to its precipitation. An additional measure towards the prevention of Fe leaching would be preliminary analysis before application and selection of substratum with low Fe content. Removal efficiencies of all WW constituents were evaluated in terms of difference between inflow and outflow concentrations from the first and the fourth CW treatment beds. Additional removal of constituents before the final outflow of treated water into the stream was assumed to be achieved when the water flowed through the polishing lagoon, an area from which samples were not taken.