Study On The Modified IC Anaerobic Reactor For Treatment Of Dyeing Wastewater

The internal circulation anaerobic reactor(IC anaerobic reactor) is a typical third-generation anaerobic reactor based on the UASB reactor, which was developed by the PAQUES company from the Netherlands in mid 80’s. Less biogas produced during the start-up of IC reactor being used to treat poorly biodegradable organic wastewater resulted in insufficient wastewater in the gas upflow tube to enable efficient hydraulic mixing and anaerobic sludge commonly being settled in the bottom of the reactor, affecting the mass transfer between wastewater and sludge, which limit the application range of the IC reactor. The textile dyeing industry, an important traditional pillar, produces large volumes of wastewater from different dyeing processes. So, it is important to study the treatment of dyeing wastewater. In order to overcome the limitation of the IC reactors in engineering applying, the modified IC anaerobic reactor was used to treat dyeing wastewater in this study. Comparing to the IC anaerobic reactor, the modified IC anaerobic reactor with the external circulation pipe between the first reaction zone and mixed zone improved hydrodynamics and mass transfer between substrate and sludge, resulting in the increase of the reactor treatment efficiency. The results are summarized as followings:In this study, granular sludge was used as the seed sludge. The proportion of dyeing wastewater in influent was gradually increased to domesticate sludge under the external circulation flow rate of 420 L/h, and the reactor was completed the start-up in day 48. With the increase of the proportion of dyeing wastewater, the COD removal efficiency decreased from 93.8% to 85%, but the VFA in effluent increased. The OLR then gradually increased from 4.8 kg COD/(m3·d) to 9.6 kg COD/(m3·d) as a result of the increased inflow rate and influent COD concentration, and the average COD removal efficiency reached 75% with a peak value of 87.2%, the biogas production increased from 1.5 L/(L·d) to 2.92 L/(L·d). At the end of the stable stage, the COD removal rate reached 85% for the OLR of 8.4 kg COD/(m3·d), with the VFA in effluent below 200mg/L.The optimal external circulation flow rate of the MIC anaerobic reactor was 420 L/h(the corresponding upflow velocity was 23.9 m/h), and the COD removal efficiency could reached 85% under the optimal external circulation flow rate. The low upflow velocity(0.1 m/h)would result in incomplete mixing between sludge and substrates and the creation of dead zones in the reactor, which led to the decrease of the COD removal efficiency. However, excessive upflow velocity(40.9 m/h) enhanced the mutual collisions between granular sludge, which resulted in fracturing of the sludge.The characterizations of inoculation sludge and granular sludge in stable stage were studied, and it was found that the granular sludge granularity distribution had changed and the sludge size increased as the reaction proceeded, with the portion of particles > 2 mm increasing from 77.9% to 85.5%. The surface of granular sludge was rough and had many deep holes. A lot of methanogens occurred in inoculation sludge and granular sludge in stable stage, such as Methanobacterium, Methanolinea and Methanosaeta.The kinetic models of the MIC reactor under the upflow velocity of 23.9 m/h and 0.1 m/h were studied, and it was found that Grau second-order and Modified Stover-Kincannon model could be applied in the design of the MIC reactor, with high correlation coefficient value(R2>0.98).