Methanogen Populations Optimized Adsorption-Biodegradation Anaerobic Sequencing Batch Reactor

ASBR has gradually been adopted widely both in the domestic and overseas in treating many kinds of wastewater owing to the abilities of granulation, adaptation to large wastewater concentration range and flexible operation. Since the dominant biomass in the reactor has no stabilization, the effluent from ASBR always needed to treat by aerobic method sequentially. Thus, ASBR still has economic potential to bring into play. Here, a new anaerobic technology in treating wastewater—Adsorption-Biodegradation Anaerobic Sequencing Batch Reactor (AB-ASBR) has been developed aiming at overcoming these limitations. The study of its start-up, operation mode and appropriate process conditions was concluded as follows:1. During the adsorption duration, the operation mode of AB-ASBR was fill-adsorb-drain-settle-regenerate. While during the biodegradation duration, the operation mode was fill-react-settle-drain. When the sludge in the reactor granulated, the different preponderant biomass began to predominate in each column of the reactor under AB-ASBR operation mode for some time. The semi-saturation constants (KS) of each column were calculated. The KS of column A was 1.83mmol, which was much larger than the KS of column B, 0.05mmol. Combining with the results of scanning electron micrograph(SEM) and Gram stain pictures, it was demonstrated that in adsorption column (column A), Methanosarcina was the predominated bacteria, while, in the biodegradation column (column B) Methanothrix was the predominated bacteria. The optimization of biomass populations will be propitious to enhance OLR and the drainage quality.2.Using milk powder as substrate, changes of COD, VFA, biogas, MLSS and MLVSS during the reaction process were monitored at low COD inflow concentrations (1000mg/L,1333mg/L and 2000mg/L). The results showed that the biomass gradually increased with the enhancement of COD concentration, at the same time, the activity of the granular sludge improved with the increasing times of AB-ASBR operation.The optimal adsorption duration under the three concentrations was all 20min. The regeneration duration was 6h, and the biodegradation duration was 2.5~4h, when the concentrations of COD in each column were below 100mg/L. It could be confirmed that when the regeneration duration ended in column A, the biodegradation reaction has completed already. In order to acquire better result, the reaction duration could prolong befittingly. Considering the cubage utilization ratio, the dimension of column B should be reduced or the column A be augmented. Thus, the regeneration will finish at the moment of the completion of biodegradation.The determining results showed that the main gases were H2 and CH4 in the biogas produced, and CH4 accounted for 72%~76%.3. OLR was enhanced step by step when AB-ASBR operated steadily. The COD concentrations in the inflow were increased ranging from 3000mg/L to 7500mg/L. The adsorption characteristic of the granular sludge and its relation with the amount of biomass were investigated. It was indicated with the enhancement of COD concentration, the maximum adsorption time shortened ranging from 20min to 5min. That was to say when the organic substrate concentration increased, the amount of biomass in the reactor manifold correspondingly, so the adsorption duration shortened.SLR has positive correlativity with the adsorption amount. When SLR was higher, the impetus of mass transfer larger, and the adsorption amount of the granular sludge lager. Within certain SLR (range from 0.3gCOD/(gMLSS·d) to 0.5gCOD/(gMLSS·d)), the adsorption ratios of the granular sludge increased with the enhancement of SLR (ranging from 67% to 90%). After that, the ratio was kept at more than 90% level constantly.At concentration of 7500mg/L, the maximum adsorption effect could obtain rapidly at 5min no matter whether the reactor was stirred by the biogas continuously, intermittently or without agitation at all because of the fine activity of the granular sludge, and the maximum adsorption ratios were 67%,65.7% and 65.7%, respectively. In order to save energy, draining could take place at 5min after the filling of wastewater with no agitation.The adsorption characteristic of the granular sludge could improve with regeneration. The longer of the regeneration duration, the larger of the adsorption amount and ratios of the granular sludge obtained. But they wouldn't change any more after 6h.The maximum adsorption ratio of the granular sludge would also improve with proper idle. But the biomass decreased with too long idle duration because of the occurring of endogenesis respiration. Although the adsorption ratios ascended, 3 hours'idle was too long to the whole reaction cycle and could cause the reactor's cubage utilization ratio descended. Therefore, in case of wastewater flow breaking down, proper idle duration controlled within certain range should be noticed.4. The influences of such factors as filling duration, stay duration before draining(TA), wastewater quality and OLR on the performance of AB-ASBR were investigated. The results were as follows:Different filling duration caused different maximum adsorption time and adsorption ratios. When the filling duration was no more than 15min, the maximum adsorption time appeared at 25min with the largest COD removal ratio (89.2%) and lowest VFA value (84mg/L). When the filling duration was prolonged to 45min, the maximum adsorption time appeared at 30min.The drainage quality varied with the wastewater stay duration before draining. The best COD removal ratio (96.8%) has been obtained when TA was 30min. But the lowest VFA value has been observed when TA was 60min, which was in favor of preventing acidification when AB-ASBR operated under much higher OLR.The higher the ratio of colloid substance in the inflow, the longer the time to arrive to maximum adsorption and the larger COD removal amount having been got. When the colloid substance ratios (CODcol/CODt) increased from 30% to 50%, the maximum adsorption time prolonged from 25min to 45min, and the COD removal ratios improved from 86.8% to 89.1%. The biodegradation duration in column B prolonged accordingly with colloid ratio's enhancement. The COD concentrations in the drainage were all less than 100mg/L.The COD removal ratio increased with the enhancement of OLR within certain range, which indicated that AB-ASBR has good adaptation ability, although the reaction duration would augment.5. The granular sludge has good sedimentation performance in high speed reactors in which the sludge was granulation, which could cause sediment in the reactor's bottom. This has no good for the solid–liquid mass transfer and the mass transfer in liquid phase. Agitation will benefit to the contact between substrate and biomass, shorten reaction duration and prevent the accumulating of the volatile acid in local reactor.According to the analysis of COD,VFA,MLSS,MLVSS and photographs, the effects of three agitation manners within the same stirring duration on AB-ASBR were investigated, which was stirred by the biogas produced itself and fed with the synthetic wastewater with the chemical oxygen demand (COD) concentration of 16500mg/L. It was indicated that the size of the granular sludge reduced from 2~3mm to 0.5mm with the increasing mixing intension. According to SEM, too much agitating intension could destroy the structure of the granular sludge, which caused the large granules to become into small ones. The condition of 3min/30min was chosen as the optimal agitation intension, which could maintain the granular sludge appropriate dimension and configuration and get best operation effect.6. According to the changes of COD concentration during adsorption, regeneration and biodegradation duration, it was concluded that during the granular sludge adsorption process, the membrane transfer mass was the limit speed step. The adsorption process could be described with pseudo-second-order model.7. The two technologies ASBR and AB-ASBR were contrasted.Dispending on the same COD concentration (2000mg/L) in inflow, all the intermittent fermentation reactions such as adsorption, hydrolysis, and acidification and so on happened in ASBR, in which the granular sludge was made up of hydrolytic bacteria, acidogenic bacteria and methanogenic bacteria. Thus, no matter how long the reaction duration prolonged, the COD value could only decrease to about 400mg/L at most. However, Methanothrix was the optimal biomass in column B of AB-ASBR, which could benefit to remove organic substance drastically. COD in the drainage from column B was below 100mg/L, which measured up the 2nd standard of the contamination let criterion of town sewage plant (GB18918-2002) (COD≤100mg/L). The drainage quality was enhanced remarkably.Under both low concentration experiment and high concentration comparing with the literature reported, AB-ASBR testified to have better wastewater-treating effect and shorter HRT, which could improve the reactor's cubage utilization ratio. Thus the cost could be saved observably.