Improvement of anaerobic digestion of municipal wastewatertreatment plant sludges and lignocellulosic substrates in biogas production

Namen doktorske disertacije je izboljšati tvorbo metana z mehanskimi in encimskimi predobdelavami substratov. Za anaerobno presnovo različnih substratov in določevanje biometanskega potenciala smo uporabili napravo Automatic Methane Potential Test System (AMPTS II). AMPTS II je analitična naprava laboratorijske skale, ki omogoča meritve ultra nizkih hitrosti tvorbe biometana, proizvedenih med anaerobno presnovo biološko razgradljivih substratov. Donosnost bioplinskih elektrarn je omejena na konkretne primere, ki jih je težko posplošiti na zbrane podatke v literaturi, saj ti zajemajo različno modificirane substrate, ki so jim zmanjšali velikost delcev ali jih kemično predobdelali in s tem posledično spremenili njihove lastnosti in energetski prirastek. Zato za konkretne odločitve na bioplinarnah potrebujemo podatke, ki izhajajo iz inokuluma konkretne bioplinske naprave in substrate v takem stanju, kot se jih dozira v anaerobne reaktorje na realnem modelnem merilu. Z nadgradnjo komercialnega sistema AMPTS II iz 0,5 l velikosti na 5 l modelno merilo smo razvili in validirali napravo za eksperimente, kjer lahko uporabljamo realni inokulum iz realne bioplinske naprave in realne substrate v takšni obliki kot jih dozirajo v anaerobne reaktorje na bioplinarnah. Na 5 l pilotnem modelnem merilu smo ocenili biometanski donos 24 substratom, ki so bili v trdni in tekoči obliki in jih primerjali z že obstoječimi objavljenimi podatki. Z dodajanjem različnih aditivov v obliki encimov in mikroorganizmov v proces anaerobne presnove, smo ocenili vpliv na nastajanje metana in izboljšali tvorbo metana. S kombinacijo različnih substratov, ki so jih sestavljali papirniško blato iz Kraft procesa, dehidrirano papirniško blato, biološki odpadki in lignocelulozni substrat, smo v šaržnih sistemih optimizirali tvorjenje metana. V semi-kontinuiranih procesih, kjer smo uporabili dehidrirano papirniško blato iz Palome, smo testirali vpliv delovanja encimov na tvorjenje metana, kjer smo dosegli občutno povečanje tvorbe metana, v naslednjem semi-kontinuiranem procesu pa smo testirali ultrazvočno predobdelavo blata iz ČN v kombinaciji z dodajanjem hidrolitskih encimov. Spremljali smo tudi delovanje bioplinske elektrarne (BPE) Vučja vas v obdobju 5 mesecev, ko je sestava vhodnih substratov nihala. S tehniko T-RFLP smo preučili vpliv encimov in čas inkubacije na strukturo bakterijske in arhejske združbe. Z uporabo programske opreme STATISTICA smo predvideli optimalne kombinacije substratov pri šaržnem načinu delovanja.The aim of this doctoral dissertation was to improve the production of methane by mechanical and enzymatic pretreatments of organic substrates. For anaerobic digestion of different substrates and determination of biomethane potential, Automatic Methane Potential Test System (AMPTS II) device was used. AMPTS II is an analytical laboratory scale device used in measurements of ultra low speed production of biomethane produced during the anaerobic digestion of biodegradable substrates. Although biogas yields of biogas plants arelimited to the specific substrates, methane yields are difficult to generalize from the collected data in published literature due to different modifications of substrates, including particle size reduction or chemical pretreatment all affecting their properties and energy recovery. Therefore, for biogas plant decision making the data need to be derived from inoculum of concrete biogas plant and substrates in such a condition as to be dosed in anaerobic reactors on real industrial scale. By upgrading commercial system AMPTS II from 0.5 liters to 5 liters, a pilot scale device was developed and validated for such real-scale experiments mirroring anaerobic reactors at the biogas plant. On 5 liter pilot scale biomethane yield of 24 substrates in solid or liquid form was assessed and compared with existing published data. By adding a variety of additives in the form of enzymes and micro-organisms in the process of anaerobic digestion, the impact on the production of methane and enhancement of the production of methane was evaluated. A combination of different substrates from paper mill sludge from Kraft process, a dehydrated paper mill sludge, bio-waste and lignocellulosic substrate an optimization of methane production in batch mode was conducted. The effects of the addition of hydrolytic enzymes on the production of methane from dehydrated paper mill sludge from Paloma was further tested in semi - continuous experiments. Significant improvements were detected. In the next following semi - continuous experiments an ultrasonic pre-treatment of sludge from the treatment plant in combination with the addition of hydrolytic enzymes was tested. In addition, the operation of the biogas plant Vučja vas was monitored for a period of 5 months during the substrate fluctuation period. Using T- RFLP technique the effects of enzyme and incubation time on the structure of bacterial and archeae consortium were assessed. By using software STATISTICA an optimal combinations of substrates in a batch mode were determined