A Review of the Processes, Parameters, and Optimization of Anaerobic Digestion
Total Page：16
File Type：pdf, Size：1020Kb
International Journal of Environmental Research and Public Health Review A Review of the Processes, Parameters, and Optimization of Anaerobic Digestion Jay N. Meegoda 1,* , Brian Li 1,2, Kush Patel 1 and Lily B. Wang 2 1 Department of Civil and Environmental Engineering, New Jersey Institute of Technology, Newark, NJ 07102, USA; [email protected] (B.L.); [email protected] (K.P.) 2 The Pingry School, Basking Ridge, NJ 07920, USA; [email protected] * Correspondence: [email protected]; Tel.: +1-973-596-2464 Received: 17 September 2018; Accepted: 7 October 2018; Published: 11 October 2018 Abstract: Anaerobic digestion is a technology that has been used by humans for centuries. Anaerobic digestion is considered to be a useful tool that can generate renewable energy and significant research interest has arisen recently. The underlying theory of anaerobic digestion has been established for decades; however, a great deal of current research is directed towards the optimization of anaerobic digestion under diverse digestion conditions. This review provides a summary of the processes underlying anaerobic digestion, commonly-utilized measurements of anaerobic sludge, operating parameters of anaerobic digesters, and methods of acceleration and optimization used to improve process efficiency. Recent developments in addition to older research are considered to provide a general but comprehensive summary of accumulated knowledge in the theory of anaerobic digestion, as well as considerations in the efficient operation of digesters. We have determined that the numerous factors pertinent to the design and operation of batch-based anaerobic digesters must each be considered to ensure the maximum efficiency and cost-effectiveness of a digester provided its respective operating conditions. Keywords: anaerobic digestion; biogas; energy; food waste; optimization; parameters; processes 1. Introduction Historical evidence from Assyria and Persia indicates the use of biogas for heating bathing water as early as the 10th century B.C.E. (Before Common Era, i.e., B.C.) [1]. In the Middle Ages, Jean Baptiste van Helmont observed the production of combustible gas from the decomposition of organic matter in lakes [2]. Later on, Alessandro Volta conducted a series of experiments on combustible gas that was collected from marsh sediments, observing a direct correlation between degraded organic matter and gas production [3]. In 1808, Humphry Davy discovered that anaerobically digested cattle manure produced methane, which aroused the possibility of producing combustible gas from manure [1]. Current waste management practices in the United States allows for significant methane emissions. In 2015, landfills, animal waste treatment, and wastewater treatment constituted the third, fourth, and seventh largest sources of methane emissions, respectively (Figure1), collectively being culpable for roughly 45% of methane emissions as a carbon dioxide equivalent [4]. However, infrastructure that supports anaerobic digestion is not only able to reduce greenhouse gas emissions, but can also generate renewable energy and divert organic wastes from landfills [5]. Currently, there exist over 2000 facilities producing biogas in the United States; however, that number could climb to over 11,000 provided that proper support is afforded [6]. Nonetheless, anaerobic digestion still faces a series of social and economic obstacles that prevent its full potential from being leveraged, although market conditions are becoming increasingly favorable to anaerobic digestion [7,8]. Int. J. Environ. Res. Public Health 2018, 15, 2224; doi:10.3390/ijerph15102224 www.mdpi.com/journal/ijerph Int. J. J. Environ. Environ. Res. Res. Public Public Health Health 2018,2018, 15,15, x 2224 2 of 16 Figure 1. The 2015 methane emissions sources in the United States by percentage [4]. Figure 1. The 2015 methane emissions sources in the United States by percentage [4]. The objective of this research is to develop a small-scale anaerobic digester for schools and restaurantsThe objective to compost of this food research waste while is to recovering develop a biogas small-scale to meet anaerobic their energy digester needs. for The schools food waste and restaurantsdegradation to will compost be optimized food waste via anaerobic while recoveri digestionng biogas followed to meet by aerobic their compostingenergy needs. after The biogas food productionwaste degradation is reduced. will Thebe optimized expected prototypevia anaerobic that woulddigestion result followed from this by researchaerobic composting would be a after food wastebiogas digester production containing is reduced. the following The expected chambers: prototyp (1)e a that food would waste shredder,result from (2) this an airtightresearch and would heated be aanaerobic food waste digester digester with containing an auger forthe mixing, following (3) anchambers: aerobic chamber(1) a food with waste an auger,shredder, and (2) (4) an a compost airtight andstorage heated bin. anaerobic The generated digester biogas with can an be auger connected for mixing, to the gas(3) an line aerobic via a pressure chamber equalizer, with an auger, and excess and (4)effluent a compost can be storage discharged bin. to The the generated sewers. biogas can be connected to the gas line via a pressure equalizer,This reviewand excess aims effluent to provide can be an discharged overview of to several the sewers. selected topics that have been extensively investigatedThis review in anaerobic aims to provide digestion. an Conceptualoverview of information several selected and researchtopics that findings have been aim toextensively provide a investigatedcomprehensive in anaerobic summary digestion. of developments Conceptual in anaerobic information digestion, and research both early findings and recent.aim to provide Section2 a providescomprehensive an overview summary of theof developments four stages of in anaerobic anaerobi digestion,c digestion, summarizing both early and the recent. biochemistry Section of2 providesanaerobic an digestion overview in addition of the four to providing stages of a anae briefrobic discussion digestion, of the summarizi inhibitionng sources. the biochemistry With the stages of anaerobicof anaerobic digestion digestion in introduced,addition to Sectionproviding3 proceeds a brief todiscussion review some of the of theinhibition tests used sources. in quantifying With the stagesanaerobic of anaerobic digestion, digestion particularly introduced, of the sludge Section and 3 proceeds substrates to used. review Section some 4of then the summarizestests used in quantifyingseveral areas anaerobic design considerations digestion, particularly for digesters of the and sludge further and delves substrates into a discussionused. Section of process4 then summarizesefficiency. Finally, several Section areas5 design provides considerations an overview for of severaldigesters common and further pretreatments delves into that a discussion can be used of processto increase efficiency. the process Finally, efficiency Section and 5 provides reduce digestion an overview times. of Aspectsseveral common of this accumulated pretreatments knowledge that can becan used be applied to increase to develop the process small-scale efficiency single-stage and reduce batch digestion digesters. times. Figure Aspects2 provides of this accumulated a schematic knowledgerepresentation can of be such applied a digester. to develop small-scale single-stage batch digesters. Figure 2 provides a schematic representation of such a digester. Int. J. Environ. Res. Public Health 2018, 15, x 3 of 16 Int. J. Environ. Res. Public Health 2018, 15, x 3 of 16 Int. J. Environ. Res. Public Health 2018, 15, 2224 3 of 16 Figure 2. The anaerobic digestion influent and output streams. 2. Stages of Anaerobic Digestion The process of anaerobicFigure 2.digestionThe anaerobic takes digestion place influent through and output four streams. successive stages: hydrolysis, Figure 2. The anaerobic digestion influent and output streams. acidogenesis,2. Stages acetogenesis of Anaerobic, and Digestion methanogenesis; the anaerobic digestion process is dependent on the interactions2. Stages between of Anaerobic the diverse Digestion microorganisms that are able to carry out the four aforementioned The process of anaerobic digestion takes place through four successive stages: hydrolysis, stages [9]. In single-stage batch reactors, all wastes are loaded simultaneously, and all four processes acidogenesis,The process acetogenesis, of anaerobic and methanogenesis;digestion takes theplace anaerobic through digestion four successive process isstages: dependent hydrolysis, on the are allowedinteractionsacidogenesis, to occur between acetogenesis in the the diversesame, and methanogenesis; microorganismsreactor sequenti the that anaerobically; are ablethe digestion tocompost carry out process theis then four is dependent aforementioned emptied on after the at the conclusionstagesinteractions of [9a]. given In between single-stage retention the batchdiverse period reactors, microorganisms or all the wastes cessat are that loadedion are of able simultaneously, biogas to carry production out andthe four all four [9].aforementioned processes Figure are3 depicts a simplifiedallowedstages flow [9]. toof In occur the single-stage four in the digestion same batch reactor reactors, stages sequentially; all described wastes the are compost loadedbelow. simultaneously, is then emptied afterand all at thefour conclusion processes