Micronutrients for wastewater treatment

The results of a postal survey strongly suggested that new developments in the optimisation of biological treatment processes would greatly increase the ability of wastewater-treating industries to adapt to Direct Toxicity Assessment (DTA). Trace metals (K, Fe, Mg, Cu, Ca, Mn, Al, Zn, Mo, Co) and vitamins (biotin, niacin, pyridoxine, lactoflavin, thiamine, pantothenic acid) were the micronutrients tested. Respirometry indicated that micronutrient addition could not ameliorate macronutrient deficiencies, but could significantly improve the degradation of hard chemical oxygen demand (COD) in the wastewater (up to 4.24kg COD/kg MLS S/d, i.e. 320% of the control) with no significant effect on the air requirement of the sludge. Complex interactions between trace metals that were dosed simultaneously were evident (e.g. Ca with other metals). Several positive effects led to the conclusion that micronutrients have the potential to optimise the process performance of activated sludge plants treating industrial wastewater. Porous pots were used to trial eight of the micronutrients. The retention of biomass in the pots was increased in all cases. Improvements in the degradation of COD (up to 260% of the control) were observed while biological oxygen demand (BOD) degradation was not affected. This implied the use of recalcitrant substrate components as a food source. Toxicity tests showed that the effluents from the experimental porous pots were less toxic than the control effluents. The effects of niacin addition in activated sludge treatment of industrial waste at pilot-scale were: improved sludge handling, increased COD, ammonia, SS and phosphorus removal. Mean test system COD removal efficiency was 123% of the control. The results of phosphorus and niacin dosing at pilotscale confirmed the trends observed in the porous pots. The results at all scales indicated that micronutrient addition could be a valuable tool for companies wishing to improve aerobic biological treatment of industrial wastewaters. Interviews were used to assess the potential value of micronutrient addition in responding to DTA. Several industrialists saw micronutrient addition as a route to successful adaptation.