The treatment of solvent recovery raffinate by aerobic granular sludge in a pilot-scale sequencing batch reactor.

Mature aerobic granular sludge (AGS) was inoculated for the start-up of a pilot-scale sequencing batch reactor for the treatment of high concentration solvent recovery raffinate (SRR). The proportion of simulated wastewater (SW) (w/w) in the influent gradually decreased to zero during the operation, while volume of SRR gradually increased from zero to 10.84 L. AGS was successfully domesticated after 48 days, which maintained its structure during the operation. The domesticated AGS was orange, irregular, smooth and compact. Sludge volume index (SVI), SV30/SV5, mixed liquor volatile suspended solids/mixed liquor suspended solids (MLVSS/MLSS), extracellular polymeric substances, proteins/polysaccharides, average particle size, granulation rate, specific oxygen utilization rates (SOUR)H and (SOUR)N of AGS were about 38 mL/g, 0.97, 0.52, 39.73 mg/g MLVSS, 1.17, 1.51 mm, 96.66%, 47.40 mg O2/h g volatile suspended solids (VSS) and 8.96 mg O2/h g VSS, respectively. Good removal effect was achieved by the reactor. Finally, the removal rates of chemical oxygen demand (COD), total inorganic nitrogen (TIN), NH4+-N and total phosphorus (TP) were more than 98%, 96%, 97% and 97%, respectively. The result indicated gradually increasing the proportion of real wastewater in influent was a useful domestication method, and the feasibility of AGS for treatment of high C/N ratio industrial wastewater.

Tolerance to organic loading rate by aerobic granular sludge in a cyclic aerobic granular reactor.

Sodium acetate as carbon source, tolerance to organic loading rate (OLR) by aerobic granular sludge in a cyclic aerobic granular reactor (CAGR) was investigated by gradually increasing the influent COD. AGS could maintain stability in the continuous flow reactor under OLR⩽15kg/m(3)d in the former 65 days, and SVI, granulation rate, average particle size and water content was 21 ml/g, 98%, 1.8mm and 97.2% on the 65th day. However, AGS gradually disintegrated after the 66 th day when OLR increased to 18 kg/m(3)d, and granules' properties deteriorated rapidly in a short time. High removal rates to pollutants were achieved by CAGR in the former 65 days, but the removal rates of pollutants dropped sharply from the 66 th day. With the increase of OLR and particle size, anaerobic cores inside the granules were formed by massive dead cells, while instability of anaerobic core eventually led to the collapse of the system.

[Influence of the Application of Activated Persulfate on Municipal Sludge Conditioning].

The water content of dewatered sewage sludge can decrease at about 80% by traditional sludge dewatering technologies. High water content has negative impacts on the sequent sludge disposal with a stricter standard. The sulfate free radical SO4(*-), generated by activated persulfate, is a powerful oxidant. This article found that it could improve sludge dewatering properties by using the Fe2+ activated sodium persulfate (SPS). The results showed that when using Fe2+ 25.88 mg x g(-1) (based on dry sludge solid) and S2 O8(2-) 80 mg x g(-1) (the mole ratio of Fe2+ to S2 O8(2-) was 1.1 : 1) for sludge conditioning, it could reduce the capillary suction time (CST) and specific resistance to filtration (RSF) of sludge, increased the protein and ploysaccharide as well as the COD concentration in the filtrate. The further research showed that this method could change the zeta potential of sludge, increased the sludge particle specific surface area, and made flocs become a loose layered structure from dense clusters, which was beneficial to improve the sludge dewaterability.

[Treatment of sludge liquor produced in deep dehydration by photoelectro-Fenton process].

Photoelectro-Fenton process was developed to treat the sludge liquor produced in deep dehydration. The results indicated that pollutants could be removed efficiently from the sludge liquor. Under the optimum condition of pH 3.0, H2O2 concentration of 65.3 mmol x L(-1), FeSO4 concentration of 6.53 mmol x L(-1) [ n(Fe2+): n (H2O2) = 1:10], 7.5V, the COD removal efficiency reached 59.0 % after 20 min treatment. The removal efficiency of TOC, TN, NH: -N and TP could reach 49. 3% , 20. 6% , 73.6% and 96.5% , respectively. This study would provide the reference for photoelectro-Fenton process in real wastewater treatment.

Rapid cultivation of aerobic granular sludge in a pilot scale sequencing batch reactor.

Aerobic granular sludge which had good performance to pollutants removal was successfully cultivated within 18 days in a pilot scale sequencing batch reactor, about 25% mature aerobic granular sludge was inoculated when the setting time of activated sludge was reduced to 10 min. Anaerobic biological selector was implemented to inhibit filamentous bacteria overgrowth, where the maximum COD could reach to 1703.74 mg/L. The cultivated aerobic granular sludge was irregular and pale yellow, average particle size, SVI, SV30/SV5, PN/PS, EPS and water content were 1.58 mm, 67.64 mL/g, 0.91, 2.17, 268.90 mg EPS/g MLVSS and 98.16% on the 18th day. Mechanism of rapid granulation mainly included crystal nucleus hypothesis and selection pressure hypothesis. The inoculated aerobic granules could maintain stable under short setting time environment, making it directly as the crystal nucleus and the carriers for new particles without obvious disintegration, which eventually shortened the granulation time greatly.

The stability of aerobic granular sludge treating municipal sludge deep dewatering filtrate in a bench scale sequencing batch reactor.

Inoculated with mature aerobic granular sludge in a sequencing batch reactor, gradually increasing the proportion of municipal sludge deep dewatering filtrate in influent, aerobic granular sludge was domesticated after 84 days and maintained its structure during the operation. The domesticated AGS was yellowish-brown, dense and irregular spherical shape, average size was 1.49 mm, water content and specific density were 98.13% and 1.0114, the SVI and settling velocity were 40 ml/g and 46.5m/h. After 38 days, NO3(-)-N accumulated obviously in the reactor as lack of carbon sources. When adding 1-3g solid CH3COONa at 4.5 and 5.5h of each cycle from the 57th day, the removal rate of TN rose to above 90% after 20 days, where effective COD removal and denitrification were realized in a single bioreactor. Finally, the removal rates of COD, TP, TN and NH4(+)-N were higher than 95%, 88%, 96% and 99%.

[Research on cultivation of aerobic granular sludge and its characteristics in sequencing fed batch reactor].

Aerobic granular sludge was cultivated in the sequencing fed batch reactor, and granules' characteristic and reactor's performance to the pollutants were studied. The SFBR was operated under the conditions as: inoculated with activated sludge former self-cultivated, fed with simulated wastewater, and continuous feed/intermittent discharge and alternately anaerobic/aerobic operation mode. The results showed that through gradually decreasing the settling time, aerobic granular sludge was successfully cultivated in 28 days, which was yellow, irregular shape, and small particle size (the average particle size was 0.56 mm). Under normal circumstances, the SVI stayed under 70 mLg-1. EPS (as MLVSS) reached the maximum 373.24 mg.g-1 on the 59 d, which increased about 2.5 times over the inoculums. However, EPS decreased sharply during the later period due to the disintegration of aerobic granular sludge. MLSS was always below 3 000 mg L -1 during the middle and later periods in the reactor. During the 63 days' operation, the removal rate of COD by the reactor maintained at about 90% except the abnormal circumstances, and the effluent COD was less than 100 mg.L-1. TIN and ammonia nitrogen's removal efficiency by the reactor fluctuated greatly, and the removal rates were 44.45% -94. 72% and 43. 87% -93. 13% respectively. The removal rate of TP was between 44. 50% -97. 40% , which could remain above 60% under normal circumstances. Limited to the automatic control level, AGS was disadvantage in the competition with filamentous bacteria that overgrew easily during the long time aerobic starvation period at night, which eventually led to the collapse of AGS.

[Acceleration of the formation of aerobic granules in SBR by inoculating different proportions and different diameters of mature aerobic granules].

In the SBR reactor, the mixed traditional activated sludge and aerobic granules were used as seed sludge to cultivate aerobic granular sludge. The whole research can be divided into two phases. In the first stage, different proportions of aerobic granules (ten, fifteen and twenty percent) were added to three SBR reactors, respectively. In the second stage, aerobic granules of different sizes (unscreened, smaller than or equal to 1 mm in diameter, larger than 1 mm in diameter) were added to three SBR reactors with the proportion of twenty percent, respectively. During the cultivation, the morphological change of the sludge, variation of particle size, maturity time and removal rate of pollutants were studied. The mechanism of fast cultivation was also discussed. The results showed that the reactor with twenty percent aerobic granules had the shortest maturity time of 24 days in the first stage and the reactor with unscreened aerobic granules had the shortest maturity time of 30 days in the second stage. All the cultivated aerobic granules had a good settling property and detergency performance, with the SVI distinctly below 40 mL x g(-1) and the COD removal rate staying above 90%. The formation of aerobic granules could be divided into two stages: the accelerated disintegration stage and the disintegration and rapid forming stage.

[Rapid cultivation of aerobic nitrifying granular sludge with alternate loading method].

The nitrifying granular sludge was cultivated in three Sequencing Batch Reactors (SBR), R1, R2 and R3, respectively. There were two new cultivating methods applied in R1 and R2, which alternately changed the influent nitrogen loading and the influent carbon and nitrogen loading, respectively. The traditional method of step-increasing nitrogen loading was adopted in R3. The results showed that the full-sense nitrifying granular sludge could be cultivated successfully after 70 days in R1 and R2, while it took 147 days in R3. The denser granules with higher activity of nitrifying bacteria and better denitrifying performance could be rapidly obtained by alternately changing the influent carbon and nitrogen loading simultaneously. The removal rates of ammonia nitrogen and total nitrogen were about 95% and 70%, respectively, under the stable operation conditions. Overall, the physical and chemical properties of granules and the performance of denitrification were outstanding in R2. From the comparison results, it indicates that the increasing influent organic loading can speed up the formation of granules and their growth at the early cultivation stage.

[Research of aerobic granule characteristics with different granule age].

In the SBR reactor, we studied the different style, physicochemical characteristic, pollutants removal and microbial activity between the short age and long age aerobic granule, respectively. The short age aerobic granule was cultivated from activated floccules sludge and the other was gotten from aerobic granular sludge which was operated stably more than one year. The results indicated that the wet density, the specific gravity and integrated coefficient (IC) of the short age aerobic granule were 1.066 g x cm(-1), 1.013 g x cm(-3) and 98.7%, respectively. And that of long age were 1.026 g x cm(-3), 1.010 g x cm(-3) and 98.4%, respectively. All of them were higher than the long age aerobic granule. The mean diameters of them were 1.9 mm and 2.2 mm, respectively. The settling velocity of short age and long age aerobic granule were 0.005-0.032 m x s(-1) and 0.003-0.028 m x s(-1), respectively, and two kinds of aerobic granule settling velocity increased with the diameter increased. SVI of the former was lower. The COD removal rates of two aerobic granules were above 90%, and the NH4(+) -N removal rates of them were about 85%. The results of the COD effluent concentration, NH4(+) -N effluent concentration and the pollutants concentration in a typical cycle indicated that the short age aerobic granule had better pollutants removal efficiency. The TP removal rates of them were between 40% -90% and 32% -85%, respectively. The TN removal rates of them were about 80%. The SOUR(H) SOUR(NH4) and SOUR(NO2) of the short age aerobic granule were 26.4, 14.8 and 11.2 mg x (h x g)(-1), respectively. And that of long age were 25.2, 14.4 and 8.4 mg x (h x g)(-1), respectively. In summary, the aerobic granule had significantly different physical and chemical characteristics because of different granule age, and the short age aerobic granule exhibited better pollutants removal ability, higher microbial activity and more stability than the long age aerobic granule.

[Influence of non-ionic surfactants on sludge dewaterability].

The water content of dewatered sludge cake decreases to about 80% by current sludge dewatering technologies, which hardly satisfies the stricter standards of sludge disposal. In order to evaluate the effects of non-ionic surfactants on sludge dewaterability, two kinds of non-ionic surfactants (OPEO and APG) were studied by using two evaluation indexes, i. e. , specific resistance to filtration (SRF) and dewatering efficiency. Moreover, morphologies of conditioned sewage sludge and raw sludge were comparatively investigated. Results showed that non-ionic surfactants can decrease the particle size of sewage sludge floc and generate more homogenous and regular shape, and then improve the dewatering efficiency. APG has better effect on sewage sludge dewatering than OPEO. SRF of conditioned sludge with APG dosage of 0.05% DS decreased to 42% of SRF of raw sludge, and its dewatering efficiency was as high as 93%. Plate-frame pressure filter experiment demonstrated that, the water content of dewatered cake conditioned with APG dosage of 0.05% DS was lower by about 10% than that of dewatered cake without APG, and its dewatering efficiency reached 97%. Therefore, this research provides some reference for the application of APG in sludge dewatering.

[Study on physicochemical characteristics and denitrogenation of sludge during granulation].

The physicochemical characteristics and denitrogenation of sludge during granulation were investigated in SBR. It was revealed that the process of granulation can be divided into three stages, including formation, growth and mature stage. In the first stage, the settling ability of sludge was improved obviously, SVI decreased from 110 mL/g to 23 mL/g during the first 30 days; In the second phase, aerobic granule grew rapidly, the mean diameter increased to 0.82 mm from 0.25 mm in the following 15 days, the value of SOUR(h) decreased from 80 mg/(g x h) to 35 mg/(g x h), denitrification rate was highly improved during granulation, the removal efficiency of TN enhanced to 80% from 55%; In the last stage, the physicochemical characteristics of sludge and denitrogenation became stable, and the removal efficiency of TN could achieve 85%, that means simultaneous nitrification and denitrification was realized.

[Effect of organic loading rate on granular SBR].

The effect of organic loading rate on granular SBR was investigated. When the organic loading rate gradually reduced from 1.8 kg/(m3 x d) to 1.575, 1.125 and 0.67 kg/(m3 x d), the characteristics of granular sludge changed greatly, including disintegration of granules, washout of sludge, reduce of granulation rate and settleability of granule, shift of granule shape from regular sphericity to different shapes of asteroid and bacilliform and the increase of color deepness. The granular SBR system reached COD and TP removal rates were about 90% and 70%, respectively, which were not influenced by the reduce of organic loading rate. However, the simultaneous nitrification and denitrification could be greatly influenced by organic loading rate reduce. When organic loading rate reduced from 1.8 kg/(m3 x d) to 0.67 kg/(m3 x d), the removal rates of ammonia and TN decreased 45% and 40%, respectively.

[Effect of ammonia concentration on the characteristic of aerobic granular sludge].

The effect of ammonia concentration in influent on the characteristic of granular sludge was investigated in the granular SBR. Results indicated that the increase of ammonia concentration could induce filamentous growth. When the loading rate of ammonia was as high as 0.80 kg/(m3 x d), obvious disintegration of granules and washout of sludge were observed. However, in absent of ammonia, aerobic granules could not form either. Moreover, it was found that the increase of ammonia concentration could result in disperse structure, diameter increase, settleability and MLSS reduce of aerobic granular sludge system. The average removals of COD and TP by granular SBR could keep 90% and 70% respectively, and were not influenced by the increase of ammonia. But the activities of nitrification bacteria and denitrification bacteria were restricted seriously by the ammonia concentration increase. When loading rate of ammonia was increased from 0.48 kg/(m3 x d) to 0.80 kg/(m3 x d), the average removal rates of NH4(+) -N and TN reduced to 70% and 50%.