Hq40d single input multi meter probe

Synthetic wastewater and sludge dissolved oxygen (DO in mg L⁻¹), pH, temperature (T in °C) and electrical conductivity (EC in μS cm⁻¹) were analyzed using a HACH HQ40d single‐input multi‐meter probe (Hach Company, Loveland, CO, USA). Influent and supernatant soluble chemical oxygen demand (sCOD), phosphorous (PO₄³⁻–P), ammonium (NH₄⁺‐N) and nitrate (NO₃⁻–N) were measured using HACH vials LCK 314‐1014, LCK 348‐349, LCK 303‐304 and LCK 339‐340, respectively, according to manufacturer's instructions. Table 1 shows initial characteristics of synthetic wastewater and sludge samples. At the end of each experiment, a 50 ml sample was collected from each reactor cell and centrifuged for 15 min at 3,885g. The supernatant was then used for determining sCOD, PO₄³⁻–P, NH₄⁺–N and NO₃⁻–N. At the end of each experiment, oxygen uptake rate (OUR) was measured after cutting off aeration in all bioreactors through which the DO probe (Hach HQ40d) was immersed in the sludge and DO depletion was monitored by taking a reading every minute over a period of 15 min. The slope of the DO vs time plot represents the OUR (in mgO₂ L⁻¹ hr⁻¹).

Synthetic wastewater and sludge dissolved oxygen (DO in mgL⁻¹), pH, temperature (T in °C) and electrical conductivity (EC in μScm⁻¹) were analyzed using a HACH HQ40d single-input multi-meter probe (Hach Company, Loveland, CO, USA). A 50-mL sample was collected from each reactor cell and centrifuged for 15 min at 3885 × g. The supernatant was analyzed by measuring soluble chemical oxygen demand (sCOD), phosphorous (PO₄³⁻-P), ammonium (NH₄⁺-N) and nitrate (NO₃⁻-N) using HACH vials LCK 314–1014, LCK 348–349, LCK 303–304 and LCK 339–340, respectively according to manufacturer’s instructions. The oxygen uptake rate (OUR) was measured after cutting off aeration in all bioreactors. The DO probe (Hach HQ40d) was immersed in the sludge through which DO depletion was monitored by taking a reading every minute for 15 min. The slope of the DO vs time plot represents the OUR (in mgO₂L⁻¹ h⁻¹). The current (I) supplied by the DC power supplies was determined based on the effective surface area (A_s) of the anode and the desired operating current density (CD). Hydraulic retention time is the effective volume of aeration tank divided by the influent flowrate of wastewater.