Anaerobic Digestion

The concept of the waste biorefinery is known as one of the several energy recovery technologies capable of producing multi-products in the form of biofuels and value-added products treating different fractions of municipal solid waste (MSW). The conversion technologies such as anaerobic digestion (AD), pyrolysis, transesterification, incineration treat food, plastic, meat, and lignocellulosic wastes to produce liquid, gaseous and solid biofuels. Makkah city landfills receive about 2750 tons of waste every day. While during the Ramadan and Hajj seasons, these quantities become 3000 tons and 4706 tons per day respectively. More than 2.5 million animals were sold for slaughtering in 2014 Hajj, and their blood and organic solid waste were disposed of untreated. Similarly, around 2.1 million plastic Zam-Zam cups were wasted every day during the 2014 Ramadan time. In the first three days of 2014's Ramadan, 5000 tons of food was wasted only in Makkah municipality. Collectively, about 3853 tons of waste were generated each day during 2014 Hajj and Ramadan. The waste from Al-Haram and Al-Masha’ir (Mina, Muzdalifah and Arafat) and their surroundings was mainly composed of organics (up to 68.5%). There is no waste-to-energy facility existing in Saudi Arabia. The waste biorefinery in Makkah will divert up to 94% of MSW from landfill to biorefinery. The energy potential of 2171.47 TJ and 8852.66 TJ can be produced if all of the food and plastic waste of the Makkah city are processed through AD and pyrolysis respectively. The development of AD and pyrolysis under waste biorefinery will also benefit the economy with gross savings of 405 and 565.7 million SR respectively, totalling to an annual profit of 970.7 million SR. Therefore, the benefits of waste biorefinery in Makkah city and other parts of the Saudi Arabia are numerous including the development of renewable-energy science and research, solving solid waste problems, new businesses and job creation opportunities and minimizing environmental pollution.

A process simulation model was developed for the anaerobic digestion (AD) process used for biogas generation. Aspen Plus software was used for this purpose. The developed model predicts the production of biogas from any substrate at any given process condition. This model was validated against a variety of industrial data on anaerobic digestion. The four steps (Hydrolysis, Acidogenesis, Acetogenesis, Methanogenesis) with a total of 46 reactions that represent the AD process were simulated with appropriate kinetics. Sensitivity analysis was implemented for 5, 10, 20 and 30% substrates concentrations to increase the methane share in the biogas by studying the effects of hydrogen addition, HRT and pressure. The developed model is flexible and predicts enhancement of methane composition by hydrogen injection qualitatively and quantitatively.

ABSTRACT: Currently, the biogas sector in Western Europe is faced by rapid technical and non-technical developments and innovations, and biogas markets are growing at a considerable pace. In contrast, the biogas market in Southern and Eastern Europe is ...

Ammonia concentrations of 4 g N/1 or more inhibited thermophilic digestion of cattle manure. A stable digestion of cattle manure could be maintained with ammonia concentrations up to 6 g N/1 after 6 months of operation. However, the methane yield was reduced and the concentration of volatile fatty acids increased from 1 to 3 g/1 as acetate, compared to controls with an ammonia concentration of 2.5 g N/1. The temporary strong inhibition following an one-step increase in ammonia concentration was reduced by applying a gradual increase. The specific methanogenic activity of ammoniainhibited reactors (6 g N/l) with acetate or hydrogen as substrate was reduced by 73 and 52%, respectively. Tests of ammonia toxicity on the acetate-and hydrogenutilizing populations showed a higher sensitivity of the aceticlastic compared to the hydrogenotrophic methanogens; the specific growth rate for the aceticlastic methanogens was halved at ammonia concentrations of 3.5 g N/l, compared to7 g N/1 for the hydrogenotrophic methanogens.

The effect of temperature on the kinetic parameters involved in the main reactions of the anaerobic digestion process was studied. Batch tests with starch, glucose and acetic acid as substrates for hydrolysis, acidogenesis and methanogenesis, respectively, were performed in a temperature range between 15 and 458C. First order kinetics was assumed to determine the hydrolysis rate constant, while Monod and Haldane kinetics were considered for acidogenesis and methanogenesis, respectively. The results obtained showed that the anaerobic process is strongly influenced by temperature, with acidogenesis exerting the highest effect. The Cardinal Temperature Model 1 with an inflection point (CTM1) fitted properly the experimental data in the whole temperature range, except for the maximum degradation rate of acidogenesis. A simple case-study assessing the effect of temperature on an anaerobic CSTR performance indicated that with relatively simple substrates, like starch, the limiting reaction would change depending on temperature. However, when more complex substrates are used (e.g. sewage sludge), the hydrolysis might become more quickly into the limiting step.

Distribution and occurrence of Archaea and methanogenic activity in a laboratory scale, completely mixed anaerobic reactor treating pharmaceutical wastewaters were investigated and associated with reactor performance. The reactor was initially seeded with anaerobic digester sludge from an alcohol distillery wastewater treatment plant and was subjected to a three step feeding strategy. The feeding procedure involved gradual transition from a glucose containing feed to a solvent stripped pharmaceutical wastewater and then raw pharmaceutical wastewater. During the start-up period, over 90% COD removal efficiency at an organic loading rate (OLR) of 6 kg COD m À3 d À1 was achieved with glucose feeding, and acetoclastic methanogenic activity was 336 ml CH 4 gTVS À1 d À1 . At the end of the primary loading, when the feed contained solvent stripped pharmaceutical wastewater at full composition, 71% soluble COD removal efficiency was obtained and acetoclastic methanogenic activity decreased to half of the rate under glucose feed (166 ml CH 4 gTVS À1 d À1 ). At the end of secondary loading with 60% (w/v) raw pharmaceutical wastewater, COD removal dropped to zero and acetoclastic methanogenic activity fell to less than 10 ml CH 4 gTVS À1 d À1 . Throughout the course of the experiment, microbial community structure was monitored by DGGE analysis of 16S rRNA gene fragments. Five different archaeal taxa were identified and the predominant archaeal sequences belonged to methanogenic Archaea. Two of these showed greatest sequence identity with Methanobacterium formicicum and Methanosaeta concilii. The types of Archaea present changed little in response to changing feed composition but the relative contribution of different organisms identified in the archaeal DGGE profiles did change. r

Anaerobic digestion of cheese whey wastewaters (CW) was investigated in a system consisting of an ecological pretreatment followed by upflow anaerobic filter (UAF). The pretreatment was conducted to solve the inhibition problems during anaerobic treatment of CW caused by the amounts of fats, proteins and carbohydrates and to avoid the major problems of clogging in the reactor. The optimized ecological pretreatment of diluted CW induce removal yields of 50% of chemical oxygen demand (COD) and 60% of total suspended solids (TSS) after acidification by Lactobacillus paracasei at 32°C during 20 h and neutralization with lime. The pretreated CW was used to feed UAF (35°C). The effects of organic loading rate (OLR) and hydraulic retention time (HRT) on the pretreated CW anaerobic degradation were examined. The average total COD removals achieved was 80-90%. The performance of the reactor was depressed by increasing the COD concentration to 20 g/l (OLR = 4 g COD/l d) and the COD removal efficiency was reduced to 72%. Significant methane yield (280 l/kg COD removal) was obtained at an HRT of 2 days.

"Volatile fatty acids (VFA) including acetic, butyric, formic and propionic are extensively utilized in contemporary industry. Their commercial value is of high significance while their often derive from petroleum which is non-abundance source. Other methods for the production and recovery from these substances have been proposed and investigated.  Waste effluent streams are potential candidates for VFA recovery, especially if for their processing filtration technology will be used. Membrane filtration is an effective and efficient choice as it is a low cost, low energy, easy integrated method tested for the separation and concentration.
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