Design Of A New Kind Of Suspended Carrier Made Of Leftover Materials And Its Application In Wastewater Treatment

Suspended Carrier Biofilm Process (SCBP) is one of the wastewater treatment technologies which has rapidly developped since 1990. Many academic researches showed that the SCBP has the advantages both of attached biofilm process and of activated sludge process. It can be used in existing wastewater treatment plants to improve the treatment efficiencies without enlargement of tankage. However, the suspended carrier is too expensive to be used in many wastewater treatment plants in developing countries. This study aimed at devoloping a new kind of much cheaper suspended carrier which is made of a kind of leftover materals. The studies on biofilm features of the new suspended carrier were conducted. The removal of pollutants from wastewater was also examined through a series of parallel tests to compare this new suspended carrier with another suspended carrier which has been proved to be effective.The new suspended carrier was designed as a sphere with a diameter of 100 mm. Its specific surface area is 104 m²/m³. After 3-month running tests, it could be concluded that the design is suitable for the growth of biofilm inside the suspended carrier because of its structure. The average density of the suspended carrier with mature biofilm is 1.013 g/cm³, close to the density of water, so that the suspended carrier can be easily fluidized in bioreactor.The studies on biofilm features show that the growth of biofilm was rapid and the biomass was considerable high because of the rough and porous surface. In initial phase, with the effect of the capture of the activated sludge by rough and porous surface of the suspended carrier, the biomass achieved 1.2 g per suspended carrier after 3-day operation of bioreactor. After 12-day operation, the biomass became stable and the average biomass is 3.4 g per suspended carrier.A three-dimensional structure biofilm fluttered in water was observed inside the suspended carrier. Under the microscope, many zoogleas, protozoons and metazoans were found. The basic structure of the biofilm consisted of hyphomycetes, vorticellas and zoogleas. This special biofilm structure proved to be very effective for the removal of pollutants and able to handle the large variations in influent flow and concentrations.In comparison with another type of suspended carrier made of polypropylene with the same diameter and the almost same specific surface area, the new suspended carrier could increase the biomass from 2.1 g per suspended carrier to 3.4 g per suspended carrier. Thus, the new suspended carrier was more effective for the removal of organic pollutants. The average concentration of COD of the effluent was 23.4 mg/l with a removal rate of 91%.The studies on removal of ammonia nitrogen showed that both of the two suspended carriers in parallel tests were effective for the treatment of ammonia nitrogen with the ammonia nitrogen load of 1-1.5 g N/(m²Â·d). The efficiency of treatment decrease quickly with the increasing ammonia nitrogen load. Under the ammonia nitrogen load of 2-5.5 g N/(m²Â·d), the removal rate declined to 31-33% from the initial removal rate of 62-67%. The decline of removal rate was due to the high ammonia nitrogen load and the high organic load during the tests. The heterotrophic microorganism have the competitive advantages for O₂ and for growth space because of its much higher growth rate, so that the growth of nitrifying bacteria is stagnant due to competitive inhibition under high organic load.The phenomenons of simultaneous nitrification and denitrification were founded with the SCBP. Without including the removal of nitrogen by the sludge in effluent, the net removal of TN was 0.57 g N/(m²Â·d) with the new suspended carrier and 0.38 g N/(m²Â·d) with the polypropylene suspended carrier. The anoxic area could be produced inside the suspended carrier with the growth of thick biofilm.The studies on removal of total phosphor showed that high removal rate of phosphor could be achieved with the SCBP. The average concentration of TP in effluent was 0.7 mg/l with the corresponding removal rate of 75-78%.It is concluded that the new suspended carrier is suitable for the growth of biofilm due to its special structure and its rough porous surface, and that it could be effective for removal of pollutants, especially for the removal of organic matter. With the improvement of manufacturing process and the durability, it would have a high potential market because of its lower price.