The high-rate activated sludge (HRAS) process is a technology suitable for the removal and redirection of organics from wastewater to energy generating processes in an efficient manner. A HRAS pilot ...plant was operated under controlled conditions resulting in concentrating the influent particulate, colloidal, and soluble COD to a waste solids stream with minimal energy input by maximizing sludge production, bacterial storage, and bioflocculation. The impact of important process parameters such as solids retention time (SRT), hydraulic residence time (HRT) and dissolved oxygen (DO) levels on the performance of a HRAS system was demonstrated in a pilot study. The results showed that maximum removal efficiencies of soluble COD were reached at a DO > 0.3 mg O2/L, SRT > 0.5 days and HRT > 15 min which indicates that minimizing the oxidation of the soluble COD in the high-rate activated sludge process is difficult. The study of DO, SRT and HRT exhibited high degree of impact on the colloidal and particulate COD removal. Thus, more attention should be focused on controlling the removal of these COD fractions. Colloidal COD removal plateaued at a DO > 0.7 mg O2/L, SRT > 1.5 days and HRT > 30 min, similar to particulate COD removal. Concurrent increase in extracellular polymers (EPS) production in the reactor and the association of particulate and colloidal material into sludge flocs (bioflocculation) indicated carbon capture by biomass. The SRT impacted the overall mass and energy balance of the high-rate process indicating that at low SRT conditions, lower COD mineralization or loss of COD content occurred. In addition, the lower SRT conditions resulted in higher sludge yields and higher COD content in the WAS.
•A HRAS pilot was operated under controlled conditions to evaluate the impact of SRT, DO and HRT.•The removal of the sCOD fraction is difficult to control and minimize completely.•SRT, DO and HRT can be used to control the removal of particulate matter in the HRAS.•The SRT impacted the overall mass and energy balance of the HRAS.•At low SRT, lower COD mineralization and higher sludge yields and COD in the WAS were observed.
This work describes the development of an intermittently aerated pilot-scale process (V = 0.34 m(3)) operated without oxidized nitrogen recycle and supplemental carbon addition optimized for nitrogen ...removal via nitritation/denitritation. The aeration pattern was controlled using a novel aeration strategy based on set-points for reactor ammonia, nitrite and nitrate concentrations with the aim of maintaining equal effluent ammonia and nitrate + nitrite (NOx) concentrations. Further, unique operational and process control strategies were developed to facilitate the out-selection of nitrite oxidizing bacteria (NOB) based on optimizing the chemical oxygen demand (COD) input, imposing transient anoxia, aggressive solids retention time (SRT) operation towards ammonia oxidizing bacteria (AOB) washout and high dissolved oxygen (DO) (>1.5 mg/L). Sustained nitrite accumulation (NO2-N/NOx-N = 0.36 ± 0.27) was observed while AOB activity was greater than NOB activity (AOB: 391 ± 124 mgN/L/d, NOB: 233 ± 151 mgN/L/d, p < 0.001) during the entire study. The reactor demonstrated total inorganic nitrogen (TIN) removal rate of 151 ± 74 mgN/L/d at an influent COD/ Formula: see text -N ratio of 10.4 ± 1.9 at 25 °C. The TIN removal efficiency was 57 ± 25% within the hydraulic retention time (HRT) of 3 h and within an SRT of 4-8 days. Therefore, this pilot-scale study demonstrates that application of the proposed online aeration control is able to out-select NOB in mainstream conditions providing relatively high nitrogen removal without supplemental carbon and alkalinity at a low HRT.
It is still not proven that treatment of sewage in a wastewater treatment plant (WWTP) is (in every case) environmentally friendly. To address this matter, we have applied a state-of-the-art life ...cycle assessment (LCA) to an energy self-sufficient WWTP in Strass (Austria), its supply chain and the valorization of its ‘products’: produced electricity out of biogas from sludge digestion and the associated stabilized digestate, applied as agricultural fertilizer. Prominent aspects of our study are: a holistic environmental impact assessment, measurement of greenhouse gas emissions (including N2O), and accounting for infrastructure, replacement of conventional fertilizers and toxicity of metals present in the stabilized digestate. Additionally, the environmental sustainability improvement by implementing one-stage partial nitritation/anammox (e.g. DEMON®) and co-digestion was also assessed. DEMON on the digesters reject water leads to a considerable saving of natural resources compared to nitritiation/denitritation (about 33% of the life cycle resource input), this through the lowering of sludge consumption for N-removal, and thus increasing electricity production via a higher sludge excess. However, its N2O emission could be restrained through further optimization as it represents a large share (30–66%) of the plants' damaging effect on human health, this through climate change. The co-substrate addition to the digester resulted in no significant improvement of the digestion process but induced net electricity generation. If respective amounts of conventional fertilizers are replaced, the land application of the stabilized digestate is environmentally friendly through prevention of natural resource consumption and diversity loss, but possibly not regarding human health impact due the presence of toxic heavy metals, mainly Zn, in the digestate. The outcomes show that the complete life cycle results in a prevention of resource extraction from nature and a potential mitigation of diversity loss (though for some impact categories no quantification of associated diversity loss is possible) but it also leads to a damaging effect on human health, mainly via climate change and heavy metal toxicity. Since it is for now impossible to aggregate the impact to these different aspects in a sound manner, it is not yet possible to consider in this case the studied system as environmentally friendly. Generally, the field of LCA needs further development to present a better and single outcome.
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•LCA of an energy-positive WWTP incl. measurements of GHG and land app. of digestate.•DEMON leads to lower resource consumption but its N2O emission should be controlled.•Still unknown whether (studied) wastewater treatment is environmentally friendly.•For land app. of digestate to be env. friendly, heavy metals (Zn) should be removed.•Saving of resources through elect. production and usage of digestate as fertilizer.
A series of pilot-scale studies were performed to compare conventional high-rate activated sludge systems (HRAS) (continuous stirred tank reactor (CSTR) and plug flow (PF) reactor configurations) ...with high-rate contact-stabilization (CS) technology in terms of carbon recovery potential from chemically enhanced primary treatment effluent at a municipal wastewater treatment plant. This study showed that carbon redirection and recovery could be achieved at short solids retention time (SRT). However, bioflocculation became a limiting factor in the conventional HRAS configurations (total SRT ≤ 1.2 days). At a total SRT ≤1.1 day, the high-rate CS configuration allowed better carbon removal (52–59%), carbon redirection to sludge (0.46–0.55 g COD/g CODadded) and carbon recovery potential (0.33–0.34 gCOD/gCODadded) than the CSTR and PF configurations (28–37% COD removal, carbon redirection of 0.32–0.45 g COD/g CODadded and no carbon harvesting). The presence of a stabilization phase (famine), achieved by aerating the return activated sludge (RAS), followed by low dissolved oxygen contact with the influent (feast) was identified as the main reason for improved biosorption capacity, bioflocculation and settleability in the CS configuration. This study showed that high-rate CS is a promising technology for carbon and energy recovery from low-strength wastewaters.
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•High carbon redirection can be achieved by applying short SRT.•Minimum oxidation of COD is needed to produce EPS for efficient solids separation.•RAS aeration in HR-CS play a key role for improved biosorption.•Feast-famine in HR-CS play a key role for improved bioflocculation & carbon recovery.•Improved carbon capture (59%) was achieved in HR-CS compared to conventional A-stages.
•Domestic wastewater was treated in an A-stage system with varying SRT, HRT and DO.•The effect of EPS production on bioflocculation and settling was measured.•Highest TSS, tCOD, pCOD and cCOD removal ...was at 0.56day SRT and 1.0mg/L DO.•EPS fractions and components did not influence COD capture and redirection.
This paper quantifies the effect of varying solids retention time (SRT), hydraulic retention time (HRT) and dissolved oxygen (DO) concentrations on extracellular polymeric substances (EPS) production and subsequently effluent quality, carbon capture (bioflocculation) and carbon redirection (settling) in a high rate activated sludge A-stage system treating domestic wastewater. Two pilot-scale A-stage reactors were set-up with HRTs of 30 and 60min. Cascade DO control was used to maintain 3 DO set-points of 0.5, 1.0 and 1.5mg/L. A mixed liquor suspended solids (MLSS) concentration of 3000mg/L was maintained and the waste activated sludge (WAS) flow was varied to achieve SRTs of 0.28 and 0.56day. EPS fractions and the protein and polysaccharide concentrations of the mixed liquor were measured. Operation at the 0.56day SRT and 1.0mg/L DO resulted in the highest total suspended solids (TSS), total COD (tCOD), particulate COD (pCOD), and colloidal (cCOD) removal. The best overall performance in terms of bioflocculation (cCOD removal) and carbon capture (percent COD in the WAS) occurred at the 0.56day SRT and coincided with decreasing total EPS concentrations but the settling characteristics of the sludge were better at the 0.28day SRT. Overall, low correlations were found between EPS production and system performance. It is likely that at the high loading rate of the A-stage system, EPS production did not play a major role compared to the influence of operating parameters on effluent quality, carbon capture and redirection.
•Anammox monitoring via heme quantification, particle tracking and molecular tools.•Anammox biomass retention successfully achieved in the mainstream.•Bioaugmentation of AOB and competition of ...Nitrobacter and Nitrospira observed.•Switch in activity pattern led to simultaneous ammonia and nitrite depletion.•Repression of nitrite oxidation witnessed in the mainstream.
Sidestream partial nitritation and deammonification (pN/A) of high-strength ammonia wastewater is a well-established technology. Its expansion to the mainstream is, however mainly impeded by poor retention of anaerobic ammonia oxidizing bacteria (AnAOB), insufficient repression of nitrite oxidizing bacteria (NOB) and difficult control of soluble chemical oxygen demand and nitrite levels.
At the municipal wastewater treatment plant in Strass (Austria) the microbial consortium was exhaustively monitored at full-scale over one and a half year with regular transfer of sidestream DEMON® biomass and further retention and enrichment of granular anammox biomass via hydrocyclone operation.
Routine process parameters were surveyed and the response and evolution of the microbiota was followed by molecular tools, ex-situ activity tests and further, AnAOB quantification through particle tracking and heme measurement.
After eight months of operation, the first anaerobic, simultaneous depletion of ammonia and nitrite was observed ex-situ, together with a direction to higher nitrite generation (68% of total NOx-N) as compared to nitrate under aerobic conditions. Our dissolved oxygen (DO) scheme allowed for transient anoxic conditions and had a strong influence on nitrite levels and the NOB community, where Nitrobacter eventually dominated Nitrospira. The establishment of a minor but stable AnAOB biomass was accompanied by the rise of Chloroflexi and distinct emergence of Chlorobi, a trend not seen in the sidestream system. Interestingly, the most pronounced switch in the microbial community and noticeable NOB repression occurred during unfavorable conditions, i.e. the cold winter season and high organic load. Further abatement of NOB was achieved through bioaugmentation of aerobic ammonia oxidizing bacteria (AerAOB) from the sidestream-DEMON® tank. Performance of the sidestream pN/A was not impaired by this operational scheme and the average volumetric nitrogen removal rate of the mainstream even doubled in the second half of the monitoring campaign. We conclude that a combination of both, regular sidestream-DEMON® biomass transfer and granular SRT increase via hydrocyclone operation was crucial for AnAOB establishment within the mainstream.
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Zusammenfassung
Die Entfrachtung organischer Last am Anfang der Prozesskette und deren Umleitung in die Faulung hat sich als effiziente Möglichkeit zur Kapazitätssteigerung einer Kläranlage erwiesen. ...Das Triple-A®-Verfahren steht für Alternierende Aktivierte Adsorption (AAA) und repräsentiert eine aktivierte Vorklärung. Dieser Prozess kann in bestehende Vorklärbecken integriert werden und wird auf eine hydraulische Aufenthaltszeit von 2 h und ein Schlammalter von ca. 0,5 Tage bemessen. Verschiedene ausgeführte Anwendungsbeispiele zeigen eine bewährte Anpassung an rechteckige, quadratische und auch runde Beckengeometrien und Wassertiefen von 2,5 bis 5,0 m. Der Erfahrungsbereich dieser Anlagen reicht von Trockenwetter-Zulaufmengen von 300 m
3
/d bis 50.000 m
3
/d. Die Wirkungsgrade dieser Vorreinigung von ca. 60/25/33 in %CSB/%N/%P basieren auf Biosorption und Bioflockulation und sind deutlich höher als durch die reine Physik einer Vorklärung mit typischen Wirkungsgraden von 33/9/11 erreicht werden kann.
It is clear from the fundamental biochemical processes that nitrification of extremely concentrated ammonia loads requires—among others—(1) sufficient alkalinity to buffer acidification and (2) ...bicarbonate as the substrate for the autotrophic biomass. However, at low pH values the aeration process causes CO
2 stripping and consequently a decrease of the available inorganic carbon. In order to analyse such complex interactions, we suggest in this paper an enhanced version of the widely acknowledged IWA (formerly IAWQ) activated sludge models. These model enlargements comprise an ion-balance for the calculation of the pH value and of dissociation species, a balance of inorganic carbon and a more detailed description of the relevant N-elimination processes and their inhibitions. The model was successfully employed to optimise a treatment strategy for rejection-water and landfill leachate (500–2000
mg ammonia-N
l
−1, COD/N ratio of 0.25–4). Detailed data from two full-scale rejection-water treatment plants were used for systems identification, model calibration and validation. The results suggest that inhibition and limitation by nitrous acid (HNO
2) and unionised ammonia (NH
3) have often been overestimated. In this investigation the bicarbonate concentration proved to be crucial for the process. The optimisation of the bicarbonate concentration in the reactor could improve the nitrozation rate up to 100
mg NH
4
+-N
l
−1
h
−1.
The acclimatization of methanogens to two-phase olive mill wastes (TPOMW) was investigated in pilot fermenters started up with cattle excreta (37°C) and after changing their feed to excreta plus ...TPOMW (37°C or 55°C) or TPOMW alone (37°C) until a steady state was reached (28 days). Methanogenic diversity was screened using a phylogenetic microarray (AnaeroChip), and positive targets were quantified by real-time PCR. Results revealed high phylogenetic richness, with representatives of three out of the four taxonomic orders found in digesters. Methanosarcina dominated in the starting excreta (>96% of total 16S rRNA gene copies; over 45 times more abundant than any other methanogen) at high acetate (0.21 g liter⁻¹) and ammonia N concentrations (1.3 g liter⁻¹). Codigestion at 37°C induced a 6-fold increase of Methanosarcina numbers, correlated with CH₄ production (rPearson = 0.94; P = 0.02). At 55°C, the rise in temperature and H₂ partial pressure induced a burst of Methanobacterium, Methanoculleus, Methanothermobacter, and a group of uncultured archaea. The digestion of excreta alone resulted in low but constant biogas production despite certain oscillations in the methanogenic biomass. Unsuccessful digestion of TPOMW alone was attributed to high Cu levels inducing inhibition of methanogenic activity. In conclusion, the versatile Methanosarcina immediately adapted to the shift from excreta to excreta plus TPOMW and was responsible for the stimulated CH₄ production at 37°C. Higher temperatures (55°C) fostered methanogenic diversity by promoting some H₂ scavengers while yielding the highest CH₄ production. Further testing is needed to find out whether there is a link between increased methanogenic diversity and reactor productivity.
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