Pollution prevention in wastewater networks: development of a biological early warning device

摘要

A biological early warning system (EWS) was developed to screen wastewatercontaining nitrification inhibitors and identify nitrifying bacteria activity reductionwithout relying on absolute values of sensor signals. To do so, numerous sensors wereevaluated using a tiered approach to aid the analysis and made it easier to convey thecurrent state of the technology. The research then produced a framework for thedevelopment of an EWS and the applicability of sensors to the wastewater matrix. Theresearch identified a need for the development of a strategy and guidance that can helpin the prevention and detection of nitrification inhibitors. Initial tests focussed on sewerbiofilm N2O emissions, however, despite average nitrification rates of 19.5 g-NH4+-N.m-2.d-1the response was unreliable due to inadequate control. To address this, acirculating floating bed biofilm reactor (CFBBR) was designed as a sidestream. TheCFBBR biofilm’s toxicity response was compared to the sewer biofilm, a 2850 mg.L-1MLSS culture and a 10.5 mg.L-1MLSS culture (with equivalent biomass concentrationto the CFBBR biofilm). The cultures responded differently with an inhibitory effectscale of Cu2+ > ATU > Ni2+ > Cr6+ for CFBBR biofilm, ATU > Cu2+ > Ni2+ > Cr6+ for2850 mg L-1MLSS, ATU > Ni2+ > Cr6+ > Cu2+ for 10.5 mg.L-1MLSS and ATU > Cu2+> Cr6+ > Ni2+ for sewer biofilm. This was firstly attributed to suspended growthnitrification stimulation by Cu2+ doses up to ~45 mg.L-1resulting in a lower inhibitoryeffect. Secondly, very high Cr6+ and Ni2+ doses were required for biofilm nitrificationinhibition, due to diffusion limitations and slow transport through cell membranes. TheCFBBR biofilm response to heavy metals was characterised through N2O and CO2spikes and a post shock emissions recovery period was observed with the trend Ni2+ >Cr6+ > Cu2+ . A 10 minute hydraulic retention time allowed quick detection and steadystate nitrification rates of 0.4 g-NH4+-N.m-2.d-1despite high organic loading rates.Additionally, a suspended growth based monitor (Nitritox) was assessed as an inletworks toxicity detector. Incorporation of a Nitritox with a CFBBR based sewer monitoroffered increased robustness over a CFBBR only system and was shown to be viablesystem in catchments >200,000 population equivalent. This information is useful towater utilities so that they can plan for and experiment with upset early warningprotocols. It is also useful to manufacturers as they can determine product performanceneeds.