Hydro-cyclone Structure Optimization And Application In Degritting Of Municipal Wastewater Treatment Plants

The "sand" in municipal wastewater treatment plants refers to some particulate matterwhich have larger density，mainly including inorganic gravel，dust，fine stone，coal cinderand a small amount of organic particles，the seedcase，bone and grain，etc. The sand will bringnumerous impacts, with four of which are below, on the following processing units. First, thesewerage pipeline will block and the effectiveness of degritting in grit chamber will reduce aswell; Second, the biological treatment processes need to be dredged frequently and theaeration system is replaced frequently; Third, the sludge dewatering machine and otherequipments will wear down with higher probability; In addition, it is difficult to recyclesludge as biosolids because too much sand in sludge. At present，the sewage system is mainlyintercepting-combined system or both combined sewage system and separate sewage systemas well. Large amount of sand in the sewage system and particle size distribution is wide，sowe must find the right technology and method to remove the sand in the sewage system,especially for the sand size distribution under100microns, in order to ensure the normaloperation of the sewage system, to play fully for collecting and treatment capacity in sewagesystem.Hydro-cyclone is a kind of equipment which can separate two phase or multiphasematerials due to the density difference in the feed under the centrifugal force. It is simple inoperation，high in separation efficiency，compact structure，long service life，etc.Based on traditional hydro-cyclone structure, the overflow drain port, underflow drainport, feeding inlet，cone section structure and column structure of hydro-cyclone wereoptimally designed and fabricated in this experiment using stainless steel materials. Theoptimal design parameters for hydro-cyclone were evaluated through pilot experiments in oneof WWTPs in Qingdao by using experimental set-ups for degritting from sludge return line.At the same time，based on analysis of particle size distribution of the sand in return sludge,one scheme for sand removal were put forward in municipal wastewater treatment plants. Ahigh efficient hydro-cyclone degritting technology is proposed to deal with the sand settlingproblem in biological treatment unit by integrating hydro-cyclone on return sludge channels.In this way, sand is separated return sludge to achieve both sand removal and efficiencyincrease in biological treatment unit. Details of experimental study were as follows： (1) The optimal structure of hydro-cyclone (column diameter as100mm) which is usedfor degritting in return sludge include: the overflow pipe31mm in diameter，60mm in lengthwith bell structure for the bottom；the underflow pipe12mm in diameter；rectangulardivergent lines shape for feed pipe；parabolic cone shape；rib lines in column section with50mm interval.(2)The optimal hydro-cyclone has shown that: split ratio is reduced from4.02%to2.42%on average；Separation efficiency is increased on average from7.47%to8.69%；Average fixed separation efficiency is increased from3.72%to6.43%；The average pressuredrop is increased from0.142Mp to0.149Mp；The difference in average organic matterpercentage between overflow and underflow is increased from16.15%to23.33%.Inconclusion, the rest index of the hydro-cyclone are optimized except pressure drop after theapplication of optimized hydro-cyclone.