Vergara L 1 , Swain D 1 , Melia J 1 , Neis U 2,3 & Nickel K 2 1 Ultrawaves Reactors UK. 2 Ultrawaves GmbH, Germany & 3 Technical University of Hamburg - Harburg, Germany Introduction Sludge produced in wastewater treatment plants (WWTP) reaches 1% of the volume treated whilst the processes for sludge handling represent up to 60% of O&M costs. Moreover, the each time stricter EU Directive requirements regarding Biological Nutrient Removal (BNR) present a challenge whenever many of the facilities generate a weak sewage that can not provide adequate carbon to drive an efficient BNR which leads to external carbon sources, meaning significant costs and new collateral (environmental) problems to be faced. Ultrawaves ultrasound (US) technology represents a well proven solution for both issues. Disintegrated sludge is easy to biodegrade and provides with an autochthonous carbon source which leads to excess sludge reduction and BNR respectively. Metrics Sludge cell disruption is determined by the soluble Chemical Oxygen Demand COD (COD s ). The activities of hydrolytic enzymes related to the hydrolysis of the particulate COD (COD p ) is also affected by sonication. Both effects (COD s release & COD p hydrolysis) and the right US dose to be applied, play an important role in excess sludge reduction and denitrification step modelling. References Bünde WWTP is one of the full-scale installations where Ultrawaves performs on ASP + BNR. The site has a capacity of 54,000 PE and includes an alternating nitrification & denitrification process where 500 kg/d of methanol had to be dosed to reach the required nitrogen level in the final effluent. The first Ultrawaves US technology effect implies an excess sludge (WAS) reduction. The second main effect consists on the supply with an autochthonous carbon source to support an efficient denitrification process, meaning an important concept: a waste (cost) has been transformed into a resource (saving). Other positive results of sonication are the complete elimination of associated problems with bulking and foaming and an improvement in the sludge cake dewaterability. Objective This work aims to close the loop concerning US effect on Activated Sludge Process (ASP) which also includes BNR. The acquired know-how (R&D, pilot plants and full-scale installations) allows the ASP + BNR modelling. The Ultrawaves technology In aqueous media and certain frequencies and intensities, US waves produces cavitation bubbles. When these bubbles collapse, they cause mechanical shear forces capable of destroying all type of biomass. Extensive R&D and Hi-Tech standards have led Ultrawaves to the development of an US reactor which optimises biomass disintegration. Summary • Y h can be reduced from 0.67 up to 0.43 mg COD synthesized /mg COD removed . • Released COD s supports 1 st kinetic denitrification (meaning between 10 to 20% of the nitrates removed by US). • Sludge hydrolysis rate (increased by ≈ 200% through sonication) supports the 2 nd kinetic denitrification meaning the removal of the remaining nitrates (between 80 to 90%). • US dose to be applied rounds 4 kWh/m 3 . • The amount of sludge to sonicate depends on several variables (required carbon source, Stress Factor (SF), etc.). Contact details Luis Vergara [email protected] 00 44 (0) 151 424 4621 Application The application consists on the thickened waste activated sludge (TWAS) sonication and its recycling back into the AS + BNR process. TWAS sonication solubilises sludge biomass and produces more biodegradable compounds. Moreover, sludge growth yield (Y h ) and denitrification rates are enhanced. The Ultrawaves US technology has a very small footprint (1.45 m x 0.25 m) and is very easily integrated in municipal and industrial WWTP. Process modelling of excess sludge reduction and biological nutrient removal through ultrasonic disintegration of the biomass Ultrawaves US technology R&D and installations ASP + BNR modelling Disintegration of sludge biomass in WWTP. The first effect is floc deagglomeration and further sonication opens the biomass cells and releases enzymes. US effect on TWAS leads to cell lysis and cryptic growth process, where part of the new substrate is mineralised as by- product of respiration. In addition, sonicated sludge is an autochthonous carbon source to support denitrification Ultrawaves US technology may be installed in different applications within WWTPs and red circle shows the right place to optimise excess sludge reduction & BNR. Sludge reduction & BNR Before US After US By sonication of sewage sludge, biological cells are disrupted and more dissolved organic material (colloidal and soluble fractions) is made bioavailable. Dehydrogenase activity (DHA) is directly responsible for driving the e - transfer chain reaction in respiring cells and assess the biomass metabolic activity. One 5 kW US unit was installed to sonicate a TWAS flow of 1 m 3 /h (aprox. 30% of the TWAS). Sonicated flow had a TS content between 4 to 5% (TS = Total Solids). Excess sludge reduction is assessed in terms of the specific WAS production (WAS generated per COD at the inlet) with and without sonication. Nitrogen level in the final effluent is reached without an external carbon source to be added (methanol dosing was stoped) and using just sonicated sludge.