Novel Sustainable Sewage Treatment By "Organics Concentrating-Nitrogens Recovery" Process

In future,sewage treatment needs to follow sustainable development(SD)concept and pursue resoures recovery from sewage.For now,sewage treatment is generally built on conventional activated sludge process(CAS),which promotes the conversion of organic matters into CO2 by aeration and removes nitrogen and phosphorus by intensive energy/material inputs.In this paper,novel sustainable sewage treatment by “organics concentrating-nitrogens recovery” process was proposed."Organics concentrating" unit was developed to enrich organic matters with separation of organics,nitrogen and phosphorus in wastewater.In addition,“nitrogens recovery” unit improved the social nitrogen cycle sustainability,rather than removing nitrogen in destructive way.Based on the pilot scale experiments,coagulation/adsorption enhanced membrane technology for organic concentrating was evaluated.Organics concentrating and membrane fouling control was strengthened simultaneouslly.High concentrating efficiency was achieved and the average COD removal rate was 85.6±3.6%.The biochemical methane potential of the organic concentrates was 210~230 m LCH4/g COD,higher than that of excess sludge.Cake layer formed during organics concentrating play the role of pre-filtration,and thus help control the irreversible membrane fouling.Organic matter removal rate was also enhanced by cake layer.Reactor(100 ton/d)was constructed to test organics concentrating technology in large scale.Membrane fouling was effectively controlled by "adsorptive cake layer + long-run low flux mode + pulse aeration + chemical backwash" method.Under the condition of HRT 1 h and SRT 2~4 d,the transmembrane pressure maintained below 15 k Pa in one month continuous operation.Considering the low nitrogen concentration,a new “dual membrane” process was proposed.Reverse osmosis was combined with oraganic concentrating process.The pilot scale experimental results showed: effluent quality was high,satisfying the surface water class III water standard(except TN),removal of emerging pollutants(removal rate more than 91.5%)was efficient;the energy production/consumption ratio(49.2%)was significantly higher than that of the traditional process(18.5%).Ion exchange was used for nitrogen recovery.Competitive exchange between ammonium and divalent ions including calcium and magnesium was the main limiting factor.The selective removal of divalent ions by membrane capacitance deionization improved nitrogen recovery efficiency.The breakthrough volume of ammonia nitrogen increased from 57.6 ± 5.8 BV to 156.6 ± 27.6 BV,and the regeneration frequency of resin decreased obviously.At the same time,the proportion of ammonium in the regeneration liquid increased,and the total amount of nitrogen recovered in during operation cycle increased by 40%.Model based on mass balance and chemometrics indicated the organics concentrating unit play an important role in promoting energy recovery and reducing energy consumption.It was expected to become the standard step of sewage treatment process.At present,the research and application of efficient organic concentrating technology is still in its initial stage.The development of coagulation/adsorption enhanced membrane technology for organics concentrating is of great significance for sewage treatment process in future.The “organics concentrating-nitrogens recovery” process is an innovative attempt to promote the comprehensive resources recovery from sewage.