Scale-up of Innovative and Sustainable via-Nitrite Biological Processes for Resource Recovery in Existing Wastewater Treatment Plants

Over the last years, the transition from wastewater treatment plants to water resource recovery facilities has gained a lot of attention. The aim of these thesis was the deep investigation of novel via-nitrite bioprocesses for the integration of via-nitrite nitrogen and phosphorus removal from the sludge reject water with resource recovery such as nutrients, chemical precursors and high added-value bioproducts. The biological via-nitrite nitrogen and phosphorus removal from the sludge reject water through the S.C.E.N.A. process was investigated in a full-scale sequencing batch reactor (SBR) with a volume of 70 m3 located in Carbonera WWTP. Fermentation yields showed values in the range of 0.16-0.26 g CODVFA/gVSfed, while nitrogen mass balances showed that around 28-30 kg N per day were removed. At the same time, phosphorus was efficiently removed biologically, resulting in a phosphorus concentration in the sludge up to 39.7 mg P/kg TS and a daily phosphorus recovery of 1.21 kg P/day. The phosphorus-rich sludge was tested in real field and the results showed that the utilization of P-rich sludge led to similar effects on plant growth and quality parameters with respect to inorganic fertilizers. The combination of cellulosic primary sludge recovery by wastewater micro-sieving with production of bio-based volatile fatty acids in a pilot-scale platform was evaluated. The rotating belt filter allowed to separate around 50% of solids. The potential production of bio-based volatile fatty acids without pH control was 232 mgCOD/gVS and the yields further improved adjusting the initial pH to value of 9 (521 mgCOD/gVS). Semi-continuous reactor (2.6 m3) was employed and the acids production using a hydraulic retention time of 6 days was around 154 mgCOD/gVS. Conditioning primary cellulosic sludge to pH 9 enhanced volatile fatty acid production to 322 mgCOD/gVS. The utilization of the fermentation liquid fraction as carbon source for nutrients removal would reduce significantly the cost for external carbon source, while the biopolymer production would enhance the benefit from 72 to 186 €/ton TS of recovered sludge. The polyhydroxyalkanoates (PHAs) production integrated with the via-nitrite nitrogen removal from anaerobic reject water was investigated at pilot scale under long term period. Results showed that around 80% of the influent ammonia was efficiently removed by the system when both nitritation and selection SBR operated with volumetric nitrogen loading rate (vNLR) of 1.64-1.72 kgN/m3 d and 0.60-0.63 kgN/m3 d. Accumulation tests showed PHA yields ranging between 0.58 and 0.61 g CODPHA/g CODVFA, indicating an effective selection strategy. The integration of nitrogen removal and PHA production in the sidestream resulted in a methane recovery up to 4.0 m3CH4/PE y and a maximal PHA production of 1.2 kgPHA/PE y with a potential revenue for the WWTP up to 6.5 €/PE y. Data Analytics was deployed to predict the dissolved nitrous oxide (N2O) concentration in a full-scale sidestream sequence batch reactor (SBR) treating the sludge reject water. On average, the N2O emissions were equal to 7.6% of the NH4-N load and can contribute up to 97 % to the operational carbon footprint of the studied bioprocess. The results of the study revealed that the aerobic dissolved N2O concentration was correlated with the drop of average aerobic conductivity rate, the DO and the changes of conductivity between sequential cycles. Additionally, the analysis showed that N2O was always consumed after the depletion of NO2- during denitritation (after the “nitrite knee”). Based on these findings SVM classifiers were constructed to predict whether dissolved N2O will be consumed during the anoxic and anaerobic phases. The proposed approach accurately predicted the N2O emissions as a latent parameter from other low-cost sensors that are traditionally deployed in biological batch processes.