A full-scale oxidation ditch process for treating sewage was simulated with the ASM2d model and optimized for minimal cost with acceptable performance in terms of ammonium and phosphorus removal. A unified index was introduced by integrating operational costs (aeration energy and sludge production) with effluent violations for performance evaluation. Scenario analysis showed that,in comparison with the baseline (all of the 9 aerators activated), the strategy of activating 5 aerators could save aeration energy significantly with an ammonium violation below 10%. Sludge discharge scenario analysis showed that a sludge discharge flow of 250–300 m3/day (solid retention time (SRT), 13–15 days) was appropriate for the enhancement of phosphorus removal without excessive sludge production. The proposed optimal control strategy was: activating 5 rotating disks operated with a mode of "111100100" ( "1"represents activation and "0" represents inactivation) for aeration and sludge discharge flow of 200 m3/day (SRT, 19 days). Compared with the baseline, this strategy could achieve ammonium violation below 10% and TP violation below 30% with substantial reduction of aeration energy cost (46%) and minimal increment of sludge production (< 2%). This study provides a useful approach for the optimization of process operation and control.
The indicator values of microfauna functional groups and species for treatment performancewere systematically evaluated based on the continuous monitoring of the entire microfauna communities including both protozoa and metazoa over a period of 14 months, in two parallel full-scale municipalwastewater treatment systems in a plant in Beijing, China. A total of 57 species of ciliates, 14 species (units) of amoebae, 14 species (units) of flagellates and4 classes of small metazoawere identified,with Arcella hemisphaerica, Vorticella striata, Vorticella convallaria, Epistylis plicatilis and small flagellates (e.g. Bodo spp.) as thedominant protozoa, and rotifers as thedominant metazoa. The abundance of the sessile ciliateswas correlatedwith the removals of BOD 5 (Pearson's r = 0.410, p < 0.05) and COD Cr (r = 0.397, p < 0.05)while the testate amoebaewas significantly positively related to nitrification (r = 0.523, p < 0.01). At the same time, some other associationswere also identified: the abundances of the large flagellates (r = 0.447, p < 0.01), the metazoa (r = 0.718, p < 0.01) and species Aspidisca sulcata (r = 0.337, p < 0.05)were positively related to nitrification; the abundance of Aspidisca costatawas correlated to the TN (total nitrogen) removal (r = -0.374, p < 0.05 ); the abundances of the sessile species Carchesium polypinum (r = 0.458, p < 0.01) and E. plicatilis (r = 0.377, p < 0.05)were correlatedwith the removal of suspended solids.
Two full-scale systems operated in parallel,a conventional A 2 /O system consisting of anaerobic,anoxic and oxic compartments in succession and an inverted system consisting of anoxic,anaerobic and oxic compartments without internal recycle,were compared in terms of their phosphorus removal performance,with an emphasis on phosphate(P) release behaviors,using both operational data and simulation results.The inverted system exhibited better long-term phosphorus removal performance(0.2 ± 0.3 vs.0.7 ± 0.7 mg/L),which should be attributed to the higher P release rate(0.79 vs.0.60 kg P/(kg MLSS·day)) in the non-aerated compartments.The P release occurred in both the anoxic and anaerobic compartments of the inverted system,resulting in more efficient P release.Although the abundances of the 'Candidatus Accumulibacter phosphatis' population in the two systems were quite similar((19.1 ± 3.27)% and(18.4 ± 4.15)% of the total microbe(DAPI stained particles) population in the inverted and conventional systems,respectively,by fluorescence in situ hybridization(FISH)),the high-concentration DAPI staining results show that the abundances of the whole polyphosphate accumulating organisms(PAOs) in the aerobic ends were quite different(the average ratios of the poly-P granules to total microbes(DAPI stained particles) were(45 ± 4.18)% and(35 ± 5.39)%,respectively).Both the operational data and simulation results showed that the inverted system retained more abundant PAO populations due to its special configuration,which permitted efficient P release in the non-aerated compartment and better P removal.
Rong QiTao YuZheng LiDong LiTakashi MinoTadashi ShojiKochi FujieMin Yang
The effects of hydraulic retention time （HRT） on the nitrification activities and population dynamics of a conventional activated sludge system fed with synthetic inorganic wastewater were investigated over a period of 260 days. When the HRT was gradually decreased from 30 to 5 h, the specific ammonium-oxidizing rates （SAOR） varied between 0.32 and 0.45kg NH4＋-N （kg mixed liquor suspended solids （MLSS）·d）-1, and the specific nitrate-forming rates （SNFR） increased from 0.11 to 0.50kg NO3-N （kg MLSS·d）1l, showing that the decrease in HRT led to a significant increase in the nitrite oxidation activity. According to fluorescence in situ hybridization （FISH） analysis results, the proportion of ammonia-oxidizing bacteria （AOBs） among the total bacteria decreased from 33% to 15% with the decrease in HRT, whereas the fraction of nitrite-oxidizing bacteria （NOBs）, particularly the fast-growing Nitrobacter sp., increased significantly （from 4% to 15% for NOBs and from 1.5% to 10.6% for Nitrobacter sp.） with the decrease in HRT, which was in accordance with the changes in SNFR. A short HRT favored the relative growth of NOBs, particularly the fast-growing Nitrobacter sp., in the conventional activated sludge system.
Changes of protists,which were categorized into different functional groups primarily according to their feeding habits,in two full-scale municipal wastewater treatment systems experiencing sludge bulking were investigated over a period of 14 months.Protist biomass represented 3.7% to 5.2% of total biomass on average under normal sludge conditions,and the percentage increased significantly(p<0.05)under sludge bulking conditions.The biomass of Chilodonella spp.,capable of eating filamentous bacteria,tended to decrease in both systems when sludge bulking occurred,showing that the abnormal growth of filamentous bacteria did not lead to a biomass bloom of this group of protists.On the other hand,the bactivorous protists represented more than 96% of total protist biomass,and the biomass of this group,particularly the attached ciliates,increased significantly(p<0.05)when sludge bulking occurred.The significant increase of the attached ciliates may have possibly facilitated the growth of filamentous bacteria through selectively preying on non-filamentous bacteria and further exacerbated sludge bulking.The redundancy analysis and correlation analysis results showed that the biomass changes of the attached ciliates were primarily related to the sludge volume index and to some extent related to five-day biochemical oxygen demand loading and hydraulic retention time.
