IWRA Proceedings

Wastewater is a complex environment that is susceptible to a wide range of external influences leading to system variability. The dynamic nature of wastewater in both composition and inherent conditions adds another level of intricacy. Enzymes are pivotal in the removal of pollutants from wastewater so that the released end product meets the governing specifications. Developments in treatment technologies include utilising enzymes to degrade emerging micropollutants from wastewater such as bioactive chemicals (BACs). Understanding how enzymes respond to wastewater variability will allow for improved process adaption. Enzyme performance is often overlooked or the applied experimental conditions do not reflect a real wastewater treatment plant (WWTP). 

Enzymes inherent to the wastewater system and exogenous enzymes proposed in BAC treatment technologies were simultaneously studied in this work. Investigating both types of enzymes provided an overarching conclusion on process and matrix conditions that impact on enzyme behaviour linked to wastewater treatment. This included pH, temperature, solids concentration, dissolved oxygen, conductivity and metal inhibition. Hydrolases were the inherent enzymes studied due to them being responsible for degrading the main bulk of the organic sewage load. Analysing the activities of five different hydrolases provided a metabolic indicator for accessing WWTP biological performance. Unique enzyme fingerprints were derived which identified temporal and spatial variability across the sampled WWTP. For example α-glucosidase activity in the activated sludge increased by 70% from the previous sampling day and the activity across the entire treatment process varied greatly. Laccase and tyrosinase are two exogenous enzymes that are regularly put forward as BAC treatment technologies due to their high promiscuity towards different substrates. Investigating the performance of these two enzymes by BAC removal at varying conditions relevant to a WWTP informs on enzyme behaviour to system variability and in turn pollutant removal.

The EU Watch List has a number of different BACs that must be continuously monitored. In this research the selected BACs to study laccase and tyrosinase performance were estrone (E1), diclofenac (DCF) and sulfamethoxazole (SMX) as they are known endocrine disrupting chemicals. To reflect the complex nature of wastewater the substrates are investigated as single and mixed solutions when treated with laccase or tyrosinase to identify any inhibitory or enhancing effects. Previous work had shown that SMX removal increased in the presence of E1 and DCF. The degradation of the substrates by the two enzymes will move from a clean water matrix to collected wastewater samples. Research in the literature mainly focuses on using buffered solutions to represent the wastewater matrix but this does not account for the daily change in feedstock. Process factors known to influence enzyme behaviour are currently being studied and the variability analysed but in ranges typical of a WWTP. The inherent enzyme research has already shown temporal and spatial variability in activity. Furthermore the enzymes are independent of each other as different trends in activity have been observed. Standard water quality parameters are taken whilst sampling and so the next stage is to correlate these parameters with enzyme activity to identify significant relationships.