Abstract
Organic esters of phosphoric acid and other organophosphorous compounds are enzymatically hydrolyzed during wastewater treatment by microbial phosphoesterases, especially by phosphomonoesterase (phosphatase). For physiological reasons, the enzyme is inhibited by its main inorganic reaction product, ortho-phosphate. It is known that oxyanions of transition metals, resembling the molecular topology of ortho-phosphate, e.g. vanadate and tungstate, are more potent inhibitors for microbial alkaline phosphatase than phosphate. To proof this effect for activated sludge, a multitude of samples from a communal wastewater treatment plant was exposed at pH values from 7.00 to 8.50 to tungstate, vanadate, and molybdate. Inhibition effects were determined by a sensitive fluorimetric microplate assay and characteristic parameters (IC50 and IC20 concentrations) were deduced from modelled dose-response functions. Mean inhibitor concentrations (in brackets: ranges) causing 50% inactivation (IC50) at pH 7.50 were 2.5 (1.3-4.1) μM tungstate, 2.9 (1.6-5.5) μM vanadate, and 41.4 (33.6-56.7) μM molybdate. Vanadate and tungstate concentrations between 0.6 and 0.7 μM provoked a 20% (IC20) inhibition. The inhibition efficiency of tungstate and molybdate decreased with increasing pH, whereas vanadate reacted pH independently. These results underline the necessity to consider enzyme inhibition assessing the limitations and potentials of biological wastewater treatment processes.
Highlights
During wastewater treatment, most of the organic wastewater components are microbially degraded in the biological treatment stage by enzymatic hydrolysis (Nybroe et al ; Burgess & Pletschke )
Eight sludge samples collected between July 2018 and January 2019 were used to investigate the inhibition of activated sludge-associated APA by vanadate at pH 7.5 (Table 1)
The enzyme alkaline phosphatase is essential for the microbial breakdown of organic phosphorus compounds and as such decisive for the efficiency of the biological P removal from wastewaters
Summary
Most of the organic wastewater components are microbially degraded in the biological treatment stage by enzymatic hydrolysis (Nybroe et al ; Burgess & Pletschke ). Phosphohydrolases form a subgroup of this enzyme class. They preferentially cleave organic esters of phosphoric acid. Alkaline phosphatase (APA, EC 3.1.3.1), a phosphomonoesterase, has highest importance for the biotransformation of organic phosphorus compounds during wastewater treatment. It mainly hydrolyses phosphoric acid monoesters like nucleotides, terminal nucleic acid phosphate bonds, phosphoproteins and phosphorylated carbohydrates, releasing phosphorus in the bioavailable form as (ortho-)phosphate (O’Brien & Herschlag ). Synthetic organic phosphoric acid monoesters such as alkyl phosphates and phosphotensides are cleaved by APA . APA serves to secure the microbial P supply and it contributes to the elimination of phosphorus-containing trace pollutants
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More From: Water science and technology : a journal of the International Association on Water Pollution Research
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