Techno-economic analysis of sidestream ammonia removal technologies:Biological options versus thermal stripping

Over the past twenty years,various commercial technologies have been deployed to remove ammonia(NH4eN)from anaerobic digestion(AD)liquors.In recent years many anaerobic digesters have been upgraded to include a pre-treatment,such as the thermal hydrolysis process(THP),to produce more biogas,increasing NH4eN concentrations in the liquors are costly to treat.This study provides a comparative techno-economic assessment of sidestream technologies to remove NH4eN from conventional AD and THP/AD dewatering liquors:a deammonification continuous stirred tank reactor(PNA),a nitrification/denitrification sequencing batch reactor(SBR)and thermal ammonia stripping process with an ammonia scrubber(STRIP).The SBR and PNA were based on full-scale data,whereas the STRIP was designed using a computational approach to achieve NH4eN removals of 90e95%.The PNA presented the lowest whole-life cost(WLC)over 40 years,with£7.7 M,while the STRIP had a WLC of£43.9 M.This study identified that THP dewatering liquors,and thus a higher ammonia load,can lead to a 1.5e3.0 times increase in operational expenditure with the PNA and the SBR.Furthermore,this study highlighted that deammonification is a capable and cost-effective nitrogen removal technology.Processes like the STRIP respond to current pressures faced by the water industry on ammonia recovery together with targets to reduce nitrous oxide emissions.Nevertheless,ammonia striping-based processes must further be demonstrated in WWTPs and WLC reduced to grant their wide implementation and replace existing technologies.

Predicting the potential of sludge dewatering liquors to recover nutrients as struvite biominerals

Phosphorus and nutrient recovery from wastewater as mineral salts can support local replenishment of fertilisers and reduce mining,contributing to the circular economy.Wastewater and related streams are rich in nutrients,however;there is need to develop bio-based processes to recover them.This study investigates the fractions of phosphorus(P)used by Brevibacterium antiquum to form struvite biominerals(bio-struvite)in wastewater sludge dewatering liquors.After 72h of incubation,25.6 mg P/L were recovered as bio-struvite from 12.4 mg P/L organic plus condensed P and 13.2 mg P/L of orthophosphate.The potential of sludge dewatering liquors to recover nutrients as struvite was investigated by characterising ten types of sludge liquors(originating from primary,secondary sludge,feed to anaerobic digester and digestate,from 3 types of wastewater treatment plants)for their P fractions together with other parameters relevant for B.antiquum growth.Results indicated that liquors obtained from primary sludge,feed to anaerobic digesters and digestate were the most suitable to produce biostruvite,as these were found to frequently have a high content of organic and condensed P,between to 276-732 mg P/L.Liquors,from all the investigated sites,presented a higher potential for bio-struvite production than with conventional struvite precipitation.This study demonstrated that B.antiquum could convert organic and condensed P into bio-struvite,and this opens up a completely new way to recover forms of phosphorus that are not typically available for nutrient recovery in a single process.