Thesis (M. Sc. (Biochemistry, Microbiology & Biotechnology))--Rhodes University, 2004.

The UK buries about 100 million tonnes of waste a year, of which 25% is municipal solid waste (refuse). The environmental impacts from gas and leachate releases are known and direct risks to health from landfill are reported. Europe has agreed to a Landfill Directive which has set targets for the stepwise reduction in biodegradable municipal waste going to landfill. The anaerobic digestion of municipal solid waste in controlled bioreactors is an area that could play an important role in overall evolution towards sustainability by recovering biogas and organic matter. Separated hydrolysis and subsequent anaerobic codigestion was demonstrated from the literature review to have the best potential for biodegradable municipal waste diverted from landfill. The rate of hydrolysis of solids wastes remains an outstanding problem. In this research, firstly the codigestion of industrial effluent (coffee wastewater), food wastes and garden wastes were investigated for their impact on hydrolysis and digestion. The results show that there were no treatability problems for coffee wastes up to 37.5% of volume feed per day at the HRT of 9 days. The results supported the view that dilute biodegradable streams such as coffee waste may improve digestion by promoting mixing. Fruit and vegetable wastes were highly biodegradable and can have a major improvement in biogas production of the whole codigestion process, whereas garden waste was not as successful as a cosubstrate, probably because of the predominant celluloses and lignocelluloses with a low biodegradability. The literature review also revealed that washing or elutriation can remove organic matter from municipal waste. This is an important hydrolytic process in which a solubilised acidic organic matter is obtained. The codigestion of refuse hydrolysate with sewage sludge was therefore studied. A control digester treating sewage sludge only was compared with an experimental reactor fed mixed refuse hydrolysate with sewage sludge. It was possible to add the solubilised hydrolysate to existing anaerobic digesters designed at a standard sludge solids loading rate without causing overloading. (Continues...).

I Sverige förekommer strikta krav på fosforrening av avloppsvatten och detta har bidragit till att kemisk fällning har kommit att dominera som reningsmetod för fosfor vid svenska avloppsreningsverk. Fällningskemikalier är dyrt för reningsverken att köpa in och ger negativ påverkan på miljön vid tillverkning och transport. Strängare reningskrav har ökat behovet av nya reningsmetoder som på ett effektivt och miljövänligt sätt kan rena avloppsvatten från näringsämnen utan att kostnaderna för reningen blir för stora. Biologisk fosforavskiljning (bio-P) utnyttjar mikroorganismer som naturligt kan ackumulera fosfor i sina celler. En kritisk faktor för en väl fungerande biologisk fosforavskiljning är tillgången till kolkälla i form av flyktiga fettsyror (VFA). Kommunalt avloppsvatten innehåller vanligen för lite VFA för att tillgodose bio-P-processens behov. Den totala tillgången på organiskt material i avloppsvattnet är dock ofta stor och möjligheten finns därmed att genom biologisk slamhydrolys internt producera VFA. Vid biologisk hydrolys av slam utnyttjas mikroorganismers naturliga förmåga att under anaeroba förhållanden bryta ned organiskt material till mer lättomsättliga föreningar. Duvbackens avloppsreningsverk i Gävle tillämpar biologisk fosforavskiljning och producerar VFA till bio-P-processen genom primärslamshydrolys och sidoströmshydrolys av returslam. I detta examensarbete har hydrolysprocesserna vid reningsverket utvärderats med avseende på processernas förmåga att producera VFA till det biologiska reningssteget. Utvärderingen gjordes genom att mäta förändringen i halten organiskt material över hydrolysbassängerna samt genom att bedöma effektiviteten i bio-P-processen i fullskala och vid labskaleförsök. Möjligheten att stänga av primärslamshydrolysen vid verket undersöktes. Ett försök till att optimera driften av sidoströmshydrolysen gjordes genom att utföra hydrolysförsök i laboratorieskala. Resultaten indikerade att produktionen av VFA i primärslamshydrolysen var begränsad och att processen därmed bör kunna stängas av. Innan detta görs bör dock kompletterande mätningar av halten löst COD över primärslamshydrolysen utföras. Vid samtliga mättillfällen uppmättes en betydande ökning i halten organiskt material över sidoströmshydrolysen. Baserat på detta och den i examensarbetet konstaterade effektiviteten i bio-P-processen drogs slutsatsen att sidoströmshydrolysprocessen vid Duvbackens reningsverk var välfungerande. Hydrolysförsöken pekade på att ett större utbyte av VFA skulle erhållas om en kortare uppehållstid än den nuvarande användes i sidoströmshydrolysen. Detta bör vidare undersökas genom fullskaleförsök vid verket. / The strong regulations concerning phosphorus removal from wastewater in Sweden has resulted in chemical precipitation being the most common treatment method for phosphorus at Swedish wastewater treatment plants (WWTP). Precipitation chemicals are expensive and have a negative environmental impact when produced and transported. More stringent wastewater treatment requirements have increased the need of new, eco-friendly treatment methods that effectively can remove nutrients from wastewater without being too expensive. Enhanced biological phosphorus removal (EBPR) utilizes microorganisms that have the natural capability of accumulating phosphorus in their cells. A critical factor for a well-functioning EBPR-process is the availability of carbon source in form of volatile fatty acids (VFA). Municipal wastewater normally contains too small amounts of VFA to satisfy the need of the EBPR-process. The total amount of organic matter in the wastewater is on the other hand large and the possibility consequently exists to internally produce VFA through sludge hydrolysis. Biological sludge hydrolysis takes advantage of the natural capability of microorganisms to degrade complex organic compounds into easily degradable organics. Duvbacken WWTP in Gävle uses EBRP for phosphorus removal and produces carbon source through hydrolysis of primary sludge and sidestream hydrolysis of return sludge. In this master thesis the hydrolysis processes at the WWTP was evaluated with regard to the capacity of the processes to produce VFA to the biological treatment step. The evaluation was performed by measuring the change in organic material content over the hydrolysis basins and by estimating the effectiveness of the EBPR-process in full scale and by laboratory experiments. The possibility to turn off the primary sludge hydrolysis process was examined. An attempt to optimize the operation of the sidestream hydrolysis process was made by conducting hydrolysis experiments in laboratory scale. The results indicated that the production of VFA by primary sludge hydrolysis was limited and that it thus would be possible to turn off the process. Before this is done complementary measurements of COD levels over the primary hydrolysis basin should be performed. At all times considerable increments in COD content was measured over the sidestream hydrolysis basin. Based on this and the in the thesis confirmed effectiveness of the EBRP-process the conclusion was drawn that the sidestream hydrolysis of return sludge at Duvbacken WWTP was well functioning. The hydrolysis experiments indicated that a larger VFA yield would be obtained if a shorter retention time than the present was used in the sidestream hydrolysis process. This should further be investigated by experiments in full scale at the WWTP.