Techno-economic and life cycle analyses for comparison of biorefinery scenarios for the production of succinic acid, itaconic acid and polyhydroxybutyrate (PHB) from sugarcane lignocelluloses

Nieder-Heitmann, Mieke (2019-04)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

ENGLISH ABSTRACT: The pressure on energy resources worldwide combined with the awareness of the major impact industrial processes have on the environment, triggers the development of alternative energy sources and methods to reduce waste. Anaerobic digestion of waste addresses both these criteria by simultaneously supplying energy and reducing waste that would otherwise have to be stored or burned. This study focuses on the anaerobic digestion of cattle manure and the processes associated with the products downstream of the digester that can potentially replace current sources of energy and nutrients. A pilot anaerobic digester at Stellenbosch University (SU) is used as the base for the mass balance but the process data used is obtained from literature. Six different sets of processes (scenarios) were evaluated based on the possible uses of the biogas and digestate outflows from the digester. Ecoinvent’s database together with GreenDelta as Life Cycle Assessment software provider was used to determine the life cycle assessment (LCA) of each scenario. The CML impact assessment method was used as it concentrates on the LCA categories as per the scope of this study. LCA is the methodology for determining relative environmental impacts of a process from cradle to grave. The CML environmental categories are acidification potential, climate change, ozone depletion potential, photochemical oxidation, terrestrial ecotoxicity, human toxicity, depletion of abiotic resources, aquatic toxicity and eutrophication. The results of each scenario are compared to a base case consisting of the normal operation of a milk cow stall, combined with offset processes for the six scenarios. In scenario 1 and 2 the biogas is used to heat SU’s indoor swimming pool while the digestate is either applied to fields as nutrient source or cleaned via pasteurisation for domestic use. Scenario 3 uses the digestate as nutrient supply while biogas is scrubbed and bottled for cooking. Scenario 4 converts the digestate solids into fertilizer pellets while a portion of the biogas is used for generating electricity. Scenario 5 and 6 both involve the cleaning and bottling of biogas for cooking. In scenario 5 the digestate solids are mixed with limestone for fertilizer production. The liquid phase is used for irrigation. Scenario 6 uses the liquid digestate as nutrient source in a photo bioreactor cultivating algae. The bio-oil produced is converted into biodiesel. The solid digestate is applied to agricultural fields as nutrient source. After normalizing the LCA results of the scenarios against the results of the base case, it was found that the application of digestate without phase separation has a lower environmental impact than digestate converted into fertilizer. Biogas used for heating and power generation has lower impacts on the environmental categories than biogas scrubbed and bottled for cooking. The impacts from the base case are higher than the impacts of an anaerobic digester combined with processes utilizing biogas and digestate in their raw states. Processes from the different scenarios were mixed to create an optimum scenario with even lower impacts, but scenario 4’s impacts remained the lowest overall. Operating an anaerobic digester fed with cattle manure will improve the environmental impacts of a cattle stall significantly. The application of biogas and digestate on the farm adds financial benefits for the farmer while the whole operation is more environmentally friendly.

AFRIKAANSE OPSOMMING: Die druk op energiehulpbronne wêreldwyd, gekombineer met die bewustheid van die groot impak wat industriële prosesse op die omgewing het, gee aanleiding tot die ontwikkeling van alternatiewe energiebronne en metodes om afval te verminder. Anaërobiese vertering van afval spreek beide hierdie kriteria aan deur gelyktydig energie te verskaf en afval te verminder wat andersins gestoor of gebrand moet word. Hierdie studie het op die anaërobiese vertering van beesmis gefokus en op die prosesse geassosieer met die verteerder se produkte stroomaf wat potensieel die huidige bronne van energie en voedingstowwe kan vervang. ’n Loods anaërobiese verteerder is by die Universiteit van Stellenbosch gebruik as die basis vir die massabalans. Die data wat gebruik is, is uit literatuur verkry. Ses verskillende stelle prosesse (scenario’s) is geëvalueer gebaseer op die moontlike gebruike van die biogas en oorskot uitvloeisels vanaf die verteerder. Ecoinvent databasis met GreenDelta as LSA sagteware verskaffer, is gebruik om die lewensiklus assessering (LSA) van elke scenario vas te stel. Die CML impak assesseringsmetode is gekies omdat dit fokus op die LSA kategorieë volgens die raamwerk van hierdie studie. LSA is die relatiewe metodologie om omgewingsimpak van ’n proses van wieg tot graf vas te stel. Die CML omgewing kategorieë is aansuring potensiaal, klimaatverandering, osoon uitputting potensiaal, fotochemiese oksidasie, aard-ekotoksisiteit, menslike toksisiteit, uitputting van abiotiese hulpbronne, water toksisiteit en eutrofisering. Die resultate van elke scenario is vergelyk met die basisgeval wat bestaan uit die normale werking van ’n melkkoeistal, gekombineer met teenstelling prosesse vir die ses scenario’s. In scenario 1 en 2 is die biogas gebruik om die binnehuise swembad van die Universiteit van Stellenbosch te verhit terwyl die oorskot op die velde aangewend is as voedingsbron, of skoongemaak is via pasteurisasie vir huishoudelike gebruik. Scenario 3 het die oorskot as voedingstof voorsiening gebruik terwyl biogas geskrop en gebottel is om mee te kook. Scenario 4 het die vaste oorskot in kunsmiskorrels omgesit, terwyl ’n gedeelte van die biogas gebruik is vir die opwekking van elektrisiteit. Scenario 5 en 6 het beide die skoonmaak en bottelering van biogas om mee te kook, behels. In scenario 5 was die vaste oorskot met kalkklip gemeng vir kunsmis produksie. Die vloeistoffase is gebruik vir besproeiing. Scenario 6 het die vloeibare oorskot as voedingsbron gebruik in ’n foto bioreaktor wat alge kweek. Die bio-olie wat vervaardig is, is omgesit na biodiesel. Die vaste oorskot is op landbouvelde as voedingsbron aangewend. Nadat die LSA resultate genormaliseer is deur dit te vergelyk met die resultate van die basisgeval, is dit gevind dat die toepassing van oorskot sonder fase skeiding ’n laer omgewingsimpak het as ’n oorskot omgesit na kunsmis. Biogas wat gebruik is vir verhitting en kragopwekking het ’n laer impak op die omgewingskategorieë as biogas wat geskrop en gebottel is om mee te kook. Die impak van die basisgeval was hoër as die impak van ’n anaërobiese verteerder gekombineer met prosesse wat biogas en oorskot in hul rou toestand gebruik. Prosesse van verskillende scenario’s is gemeng om ’n optimale scenario te skep met selfs ’n laer impak, maar scenario 4 se impak bly oor die algeheel die laagste. Deur koeimis in ’n anaërobiese verteerder te gebruik, sal die omgewingsimpak van ’n koeistal aansienlik verbeter. Die toepassing van biogas en verwerking op die plaas hou finansiële voordele vir die boer in, terwyl die hele bedryf meer omgewingsvriendelik is.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106120
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