Obdelava anaerobnega digestata z mikroalgami in termofilna proizvodnja bioplina iz živilskih odpadkov in mikroalgne biomase

Lavrič, Lea (author), Marinšek Logar, Romana (mentor), Cirman, Andreja (comentor)

Mikroalgna biomasa je alternativna surovina za proizvodnjo biogoriv, vključno bioplina. Tehnologijo anaerobne razgradnje lahko združimo s tehnologijo proizvodnje mikroalgne biomase. Tekoči anaerobni termofilni digestat vsebuje veliko hranil, a zaradi visoke vsebnosti vode je uporaba v kmetijstvu lahko otežena in draga, prav tako čiščenja tekočega digestata na čistilni napravi. V čistilni napravi z mikroalgami uporabimo hranila iz digestata ter CO2 (izpušni plini) in odpadno toploto, ki nastajata pri izgorevanju bioplina. V raziskavi smo v pilotni napravi z mikroalgami (nadkrit odprt bazen na 89 m2) kontinuirno čistili digestat. Merili smo kvaliteto odpadne vode po mikroalgni obdelavi in spremljali prisotnost patogenov. V optimalnem obdobju smo digestat očistili do kvalitete za izpust odpadne vode v kanalizacijo. Obremenjenost digestata z organskimi snovmi (KPK 4.445 ± 973 mg O2 L-1) se je pri optimalnem delovanju zmanjšala za 81–95 % (zmanjšanje KPK do 362 ± 72 mg O2 L-1), pri čemer so mikroalge vezale dušik in fosfor iz digestata. Tekom enega leta je KPK tekočega digestata na vtoku v algno obdelavo znašal 2.317–9.552 mg O2 L-1. S testiranjem biometanskega potenciala, v digestatu proizvedenih mikroalg, smo pri termofilnih pogojih izmerili višji izplen metana iz mikroalgne biomase po termični predobdelavi (od 254,5 ± 35,5 do 406,1 ± 4,2 mL CH4 g-1 OS), prav tako pri bioaugmentaciji procesa z bakterijami C. thermocellum (176,4 ± 19,7 do 223,4 ± 5,2 mL CH4 g-1 OS) kakor tudi dobro anaerobno biorazgradljivost v kombinaciji z živilskimi odpadki (od 329,3 ± 6,7 do 497,6 ± 66,5 mL CH4 g-1 OS) glede na potencial neobdelane mikroalgne biomase (od 153,5 ± 32,2 do 168,4 ± 6,0 mL CH4 g- 1 OS). Dokazali smo ekonomsko izvedljivost algne obdelave digestata pri določenih pogojih in ocenili tveganje investicije z analizo Monte Carlo. Raziskava je doprinos k izboljšanim tehnološkim in ekonomskim rešitvam za obdelavo digestata z mikroalgami kot tudi k učinkoviti anaerobni razgradnji v tovrstnem sistemu proizvedene mikroalgne biomase.

• Language: Slovenian
• Keywords: bioplin, tekoči digestat, mikroalge, termična predpriprava, bioaugmentacija, Clostridium thermocellum, ekonomska analiza algne obdelave, analiza Monte Carlo
• Work type: Doctoral dissertation
• Typology: 2.08 - Doctoral Dissertation
• Organization: BF - Biotechnical Faculty
• Publisher: [L. Lavrič]
• Year: 2019
• PID: 20.500.12556/RUL-113430
• UDC: 606:620:628.336.6(043.3)=163.6
• COBISS.SI-ID: 9375865
• Publication date in RUL: 05.01.2020

Secondary language

• Language: English
• Title: Microalgal treatment of anaerobic digestate and thermophilic anaerobic digestion of food waste and microalgal biomass

Abstract

Microalgal biomass is a prospective substrate for biofuels, also for biogas production. Microalgal treatment of liquid anaerobic digestate and thermophilic anaerobic digestion of microalgal biomass and food waste was studied aiming to improve microalgae – biogas system. Prevalence use of biogas digestate as fertilizer in agriculture is current practice, but due to logistic and agro-technical reasons, it is often separated. Liquid fraction contains a significant portion of nutrients (especially nitrogen and phosphorous), but causes high transport costs or costs of treatment at wastewater treatment plant. The algal treatment technology can present an added value and potential economic benefit for biogas plant. Other benefits of coupling of the technologies are use of CO2 (flue gases) and waste heat. We have tested the efficiency of treatment of liquid digestate as waste water within set pilot system. Results of microalgal treatment of liquid supernatant digestate from thermophilic biogas plant, treating food waste (COD 4.445 ± 973 mg O2 L-1), in algal pond (covered system on 89 m2 with open raceway pond) shows sufficient nitrogen and phosphorous removal and COD reduction efficiency of 81–95 % (COD of effluent reduced to 362 ± 72 mg O2 L- 1) in optimum regime. Digestate organic load on inflow varied 2,317–9,552 mg O2 L-1, and was on average 4,445 ± 973 mg O2 L-1 in optimal regime. Effluent during optimal treatment (treated wastewater) is of such quality, that it can be released to the sewer. The presence of selected pathogens in algal treatment was monitored. Produced microalgal biomass was tested by methane potential assays in thermophilic process. Thermally pretreated microalgae showed higher biomethane potential (from 254.5 ± 35.5 up to 406.1 ± 4,2 mL CH4 g-1 OS), also bioaugmentation of the anaerobic digestion with bacteria C. thermocellum (from 176.4 ± 19.7 to 223.4 ± 5.2mL CH4 g- 1 OS) as native microalgae (from 153.5 ± 32.2 to 168.4 ± 6.0 mL CH4 g-1 OS). Microalgae is good co-substrate with food waste in various combinations (yield from 329.3 ± 6.7 to 497.6 ± 66.5 mL CH4 g-1 OS). Results of this thesis contribute to environment protection with the development of technology for algal treatment of digestate, including technological and economical view on feasibility of thermophilic biogas digestate treatment with microalgae and presents results of efficient pretreatment of produced algal biomass that will accelerate applicability of the solution.

• Keywords: biogas, digestate supernatant, microalgae, thermal pretreatment, bioaugmentation, Clostridium thermocellum, algal treatment feasibility, Monte Carlo simulation