Algal-Bacterial Symbiosis System Treating High-Load Printing And Dyeing Wastewater In Continuous-Flow Reactors Under Natural Light

Algal-bacterial symbiosis?ABS?system as a emerging biological wastewater treatment technology has better pollutant removal performance and lower processing costs than conventional activated sludge?CAS?system.Therefore,it has a good application prospect.Compared with domestic sewage,industrial wastewater has complex composition,high concentration of pollutants,and more difficult to degrade organic matter,which is difficult to handle,especially printing and dyeing wastewater.As an autotrophic microorganism,algae have a better removal effect on refractory organic matter and dyes.Therefore,adding algae to activated sludge to form a algal-bacteria symbiosis system for printing and dyeing wastewater has broad application prospects.In the previous study,we found that XJK-chlorella,W6-filamentous algae,and902-Selenastrum bibraianum have good removal effects on disperse blue 2BLN,malachite green and crystal violet.But like most researchers,the three algae are degrade a single dye in simulated wastewater and are not used in actual printing and dyeing wastewater.Therefore,on this basis,we mixed these three algae with activated sludge and designed a reactor that can ensure the coexistence of algae,and then processed the actual printing and dyeing wastewater,and investigate the removal effect of the algal bacteria symbiosis system on the actual pollutants in printing and dyeing wastewater.Firstly,a multi-functional integrated aerobic bioreactor with an effective working volume of 5 L was designed.The reactor consists of five parts:the influent zone,the biochemical reaction zone,the three-phase separator,the sedimentation zone and the effluent zone.At the same time,two reactors were produced.One reactor was treated with a conventional activated sludge system?CAS system?.The initial mixed liquid suspension concentration in the reactor was 1000 mg/L.One reactor used the algal symbiosis system?ABS?.System)for wastewater treatment,the initial mixture suspension solid concentration in the reactor is 1000 mg/L,the ABS system algae to sludge volume ratio is 1:1?w/w?,laboratory-cultured XJK-chlorella,a mixture of W6-filamentous algae 902-Selenastrum bibraianum,mixed with conventional activated sludge.Through a period of operation,it was found that sludge and algae were lost due to the volume ratio of the algal mud symbiosis system and the structure of the reactor,and the reaction system had a poor effect on COD removal.The volume ratio of the reactor to the algae is then optimized.The improved second-generation reactor adds a 60°slanted baffle below the right-end three-phase separator to change the direction of the water flow and reduce the impact on the sedimentation zone,allowing the sludge to flow better.The algae and activated sludge were mixed according to the volume of 1:2.After a period of operation,the MLSS value in the ABS system was kept within a certain range,and the algae content decreased,but the COD removal rate increased significantly and the chromaticity decreased significantly.The ABS system can operate stably,but there is still a certain gap between the treatment effect and the printing and dyeing wastewater treatment plant,and the volume ratio of algae to activated sludge is adjusted.The algae and activated sludge were mixed according to the volume of 1:3,and the reactor was started.After a period of operation,the ABS system was found to have a good removal effect on COD,NH₄⁺-N and chromaticity.The removal rates of COD,NH₄⁺-N and TP in ABS system were 83%,90%,35%,and the colour was between 100-120 times.The removal rates of COD,NH₄⁺-N,and TP were 8%,1%,and 2%higher than those of the CAS system,respectively,and were 10%,12%,and 8%higher than those of the biochemical stage of the printing and dyeing wastewater treatment plant respectively.The colour is reduced by40 times than the biochemical stage of the printing and dyeing wastewater treatment plant.The operating conditions of the reactor were optimized in the next experiments.This study investigated the symbiotic structure relationship between mixed algae and activated sludge and the effects of hydraulic retention time?12 h,16 h,20 h?and aeration rate?0.1-0.15,0.4-0.5 and 0.7-0.8 L/min?on ABS and CAS systems while treating high-load printing and dyeing wastewater in a continuous-flow under natural light.When the aeration rate is the same,the ABS system has the best effect on the removal of pollutants when the hydraulic retention time is 16 h.The average effluent COD,NH₄⁺-N and TP values are 95mg/L,2.4 mg/L.4 mg/L.The average COD,NH₄⁺-N and TP removal rates were 83.5%,88.6%,36.6%.Compared with the biochemical section of the dyeing wastewater treatment plant,the COD,NH₄⁺-N and TP contents were reduced by 75.2 mg/L,5.1 mg/L and 1.05mg/L,respectively,and the average COD,NH₄⁺-N and TP removal rates were increased by10.5%,10.6%and 10.5%,respectively.,the colour is reduced by 60 times.When the hydraulic retention time is 16 h and the aeration amount is 0.4-0.5 L/min,the ABS system achieves the best effect on the removal of pollutants.The average COD and NH₄⁺-N removal rate are 85.5%and 93.1%.The colour is between 100-120 times.Compared with the biochemical section of the dyeing wastewater treatment plant,it increased by 12.5%,8.6%,and the chroma was reduced by 40 times.When the aeration rate is 0.15-0.2 L/min,the dissolved oxygen of the ABS system is about 0.85 mg/L,which is 0.4 mg/L higher than the CAS system,and the aeration amount is0.4-0.5 L/min and 0.7-0.8 L/min,the dissolved oxygen of ABS system is 2.85 mg/L and 3.95mg/L,respectively,which is 0.8 mg/L higher than that of CAS system.Under low aeration and high aeration,ABS system can maintain good stability.In response to the deficiencies in the reactor and experimental conditions,the reactor was upgraded to extend the original reactor to 15 L and was protected from light in the surrounding area so that sunlight could only enter the wastewater treatment water from the upper end of the reactor.The reactor was then moved outdoors and subjected to wastewater treatment under completely natural conditions.After a period of operation,it was found that the outdoor temperature was lower,resulting in lower water temperature.At the same time,the weather caused too much rainy days,and the slight lack of illumination resulted in poor treatment.The ABS system also reduced the COD removal ability,and the removal rate was65%about.The chromaticity removal ability is correspondingly reduced,and the effluent colour is between 150-180 times.The removal of NH₄⁺-N was not greatly affected,and the removal rate was about 89%.The removal rate of total phosphorus is 35%.Although the weather affects the treatment efficiency of the ABS system,the removal level of chromaticity is consistent with that of the wastewater treatment plant,and the removal rate of NH₄⁺-N is still increased by 11%.The removal rate has increased by 10%.It is expected that the present study will provide a foundation for the practical application of ABS system,and new insights for the treatment of printing and dyeing wastewater.