In this study, by-products from alcohol production were examined in terms of their potential application as external carbon sources for enhancing denitrification in biological nutrient removal systems. Three types of batch tests were used to compare the effects of the distillery by-products, such as fusel oil, syrup and reject water, on the non-acclimated activated sludge. Much higher nitrate utilization rates (NURs) were observed for the latter two carbon sources. In the conventional NUR measurements (one-phase experiments), the observed NURs with syrup and reject water were 3.2-3.3 g N/(kg VSS h) compared with 1.0 g N/(kg VSS h) obtained for fusel oils from two different distilleries. When the carbon sources were added at the beginning of the anoxic phase preceded by an anaerobic phase (two-phase experiments), the NURs were 4.2 g N/(kg VSS h) (syrup and reject water) and 2.4-2.7 g N/(kg VSS h) (fusel oils). The heterotrophic yield coefficient, determined based on the conventional OUR measurements, varied in a relatively narrow range (0.72-0.79 g COD/g COD) for all the examined carbon sources. Due to advantageous composition (much higher COD concentrations and COD/N ratios), fusel is a preferred carbon source for practical handling in full-scale wastewater treatment plants.

Industrial waste products may be a viable alternative to commercial external carbon sources. In this study, the properties of fusel oil (distillery waste product) were investigated in terms of temperature dependency of denitrification and acclimation period. Furthermore, results obtained during three different full-scale trials were used to verify similarities with and differences from the results obtained under laboratory-scale conditions. Batch experiments with non-acclimated biomass revealed a very strong temperature dependency of the denitrification process (θ = 1.15, R(2) = 0.92) in the range of examined process temperatures (13-22 °C). Fusel oil had minor (or no) effects on the behaviour of NO2-N and PO4-P. Significantly lower nitrate utilization rates were observed during acclimation to fusel oil in the full-scale bioreactors compared to a bench-scale reactor. This may primarily be attributed to lower doses of fusel oil, lower process temperatures and more complicated process configurations (resulting in non-optimal use of fusel oil for denitrification). Results obtained from both laboratory-scale experiments and full-scale trials suggested that an acclimation period of a few weeks would be required to reach the maximum denitrification capability of process biomass, even though positive effects of dosing can be observed almost immediately.

The aim of this study was to determine the effects of chemical precipitation and addition of external carbon sources on the denitrification capability and enhanced biological phosphorus removal (EBPR) interactions at the ‘Wschod’ WWTP (600,000 PE) in Gdansk (northern Poland). For this purpose, different kinds of batch experiments were carried out with the settled wastewater (without pretreatment and after coagulation-flocculation) and external carbon sources (ethanol and fusel oil). Precipitation of colloidal and particulate organic fractions has a significant effect on denitrification and EBPR. The removal of these two fractions by coagulation-flocculation resulted in the reduced process rates (30–70%). The experimental investigations were supported by both lab-scale and full-scale simulations using a newly developed model as an expansion of the Activated Sludge Model No. 2d (ASM2d). The new model accurately predicted the effects of precipitation and external carbon addition in batch experiments. Full-scale simulations revealed that addition of external carbon source can compensate the effects of precipitation resulting in a similar NO3-N behavior compared to the reference case (without precipitation and external carbon addition). The combined effects of precipitation and addition of external carbon source resulted in a significantly different PO4-P behavior compared to the reference case.

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The effect of distillery waste product (fusel oil) as an alternative external organic carbon source (EOCS) was investigated in terms of the metabolic properties of denitrifying polyphosphate accumulating organisms (DPAOs). Samples of the non-acclimated biomass were collected from a local full-scale wastewater treatment plant employing A2/O type bioreactors. The acclimated biomass was obtained after cultivation (with fusel oil added) in a bench-scale reactor with a process configuration similar to the full-scale bioreactor. Changes in the functional properties of the biomass were investigated by measuring the phosphate release/uptake rates (PRRs and PURs), and nitrate utilization rates (NURs) with fusel oil in anaerobic-anoxic batch tests. Furthermore, a validated extended Activated Sludge Model no 2d (ASM2d) was used as a supporting tool to analyze the experimental results and estimate the contribution of DPAOs to the overall denitrification. In the non-acclimated biomass with fusel oil, the PRRs, PURs and NURs were low and close to the rates obtained in a reference test without adding EOCS. With the acclimated biomass, the PUR and NUR increased significantly, i.e., 3.5 and 2.7 times, respectively. In the non-acclimated biomass, approximately 60.0 ± 3.6% and 20.0 ± 2.2% of the total NUR was attributed to the utilization of endogenous carbon and examined EOCS, respectively. The remaining portion (20% of the total NUR) was attributed to PHA utilization (linked to PO4-P uptake) by DPAOs. With the acclimated biomass, the contribution of the EOCS to the NUR increased to approximately 60%, while the contribution of the endogenous carbon source decreased accordingly. Very accurate predictions of PURs and NURs (R2 = 0.97–1.00) were obtained with the extended ASM2d. Based on model simulations, it was estimated that the activity of DPAOs and denitrifying ordinary heterotrophic organisms corresponded to approximately 20% and 80% of the total NUR, respectively.Electronic supplementary materialThe online version of this article (10.1007/s00449-018-2022-0) contains supplementary material, which is available to authorized users.