Recent Approaches for the Production of High Value-Added Biofuels from Gelatinous Wastewater
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energies Review Recent Approaches for the Production of High Value-Added Biofuels from Gelatinous Wastewater Ahmed Tawfik 1, Shou-Qing Ni 2, Hanem. M. Awad 3 , Sherif Ismail 2,4 , Vinay Kumar Tyagi 5, Mohd Shariq Khan 6, Muhammad Abdul Qyyum 7,* and Moonyong Lee 7,* 1 Water Pollution Research Department, National Research Centre, Giza 12622, Egypt; [email protected] 2 Shandong Provincial Key Laboratory of Water Pollution Control and Resource Reuse, School of Environmental Science and Engineering, Shandong University, Qingdao 266237, China; [email protected] (S.-Q.N.); [email protected] (S.I.) 3 Department Tanning Materials and Leather Technology & Regulatory Toxicology Lab, National Research Centre, Centre of Excellence, Giza 12622, Egypt; [email protected] 4 Environmental Engineering Department, Zagazig University, Zagazig 44519, Egypt 5 Environmental Biotechnology Group (EBiTG), Department of Civil Engineering, Indian Institute of Technology, Roorkee 247667, India; [email protected] 6 Department of Chemical Engineering, Dhofar University, Salalah 211, Oman; [email protected] 7 School of Chemical Engineering, Yeungnam University, Gyeongsan 712-749, Korea * Correspondence: [email protected] (M.A.Q.); [email protected] (M.L.) Abstract: Gelatin production is the most industry polluting process where huge amounts of raw organic materials and chemicals (HCl, NaOH, Ca2+) are utilized in the manufacturing accompanied by voluminous quantities of end-pipe effluent. The gelatinous wastewater (GWW) contains a large fraction of protein and lipids with biodegradability (BOD/COD ratio) exceeding 0.6. Thus, it repre- Citation: Tawfik, A.; Ni, S.-Q.; sents a promising low-cost substrate for the generation of biofuels, i.e., H2 and CH4, by the anaerobic Awad, H.M.; Ismail, S.; Tyagi, V.K.; digestion process. This review comprehensively describes the anaerobic technologies employed for Khan, M.S.; Qyyum, M.A.; Lee, M. simultaneous treatment and energy recovery from GWW. The emphasis was afforded on factors Recent Approaches for the Production of High Value-Added affecting the biofuels productivity from anaerobic digestion of GWW, i.e., protein concentration, Biofuels from Gelatinous Wastewater. organic loading rate (OLR), hydraulic retention time (HRT), the substrate to inoculum (S0/X0) ratio, Energies 2021, 14, 4936. https:// type of mixed culture anaerobes, carbohydrates concentration, volatile fatty acids (VFAs), ammonia doi.org/10.3390/en14164936 and alkalinity/VFA ratio, and reactor configurations. Economic values and future perspectives that require more attention are also outlined to facilitate further advancement and achieve practicality in Academic Editors: Marcin D˛ebowski this domain. and Attilio Converti Keywords: gelatinous wastewater; protein degradation; anaerobic digestion; energy recovery; biofuels Received: 9 June 2021 Accepted: 3 August 2021 Published: 12 August 2021 1. Introduction Publisher’s Note: MDPI stays neutral The gelatin production in the world exceeds 375,000–400,000 tons per year which has with regard to jurisdictional claims in published maps and institutional affil- a considerable share in the economy of countries [1]. Each ton of raw materials, mainly 3 iations. bones, produces 300 m of gelatinous wastewater [2]. The gelatin industry generates huge quantities of heavily polluted wastewater containing proteins, carbohydrates, and lipids [3–6]. The gelatin processing end-of-pipe effluents have high organic contents (i.e., biochemical oxygen demand (BOD), chemical oxygen demand (COD), suspended solids (SS), and ammonia nitrogen (NH4-N) [3,4]. Moreover, the gelatinous wastewater (GWW) Copyright: © 2021 by the authors. contains high concentrations of sulfate (SO −2), calcium, and phosphorus [4,7,8]. Di- Licensee MDPI, Basel, Switzerland. 4 calcium phosphate is mainly produced during the de-mineralization process of bones [2,9]. This article is an open access article distributed under the terms and The main serious problem from gelatinous wastewater (GWW) is the odor, nuisance, conditions of the Creative Commons and that it is highly obnoxious to the habitation [2,10]. The GWW could be alkaline or Attribution (CC BY) license (https:// acidic based on the manufacturing process and the utilized raw materials [9]. GWW is creativecommons.org/licenses/by/ greasy and fibrous containing bovine bone pieces and hairs, resulting in high quantities 4.0/). of particulate organic matters [11,12]. The particulates mainly consist of animal crushed Energies 2021, 14, 4936. https://doi.org/10.3390/en14164936 https://www.mdpi.com/journal/energies Energies 2021, 14, x FOR PEER REVIEW 2 of 19 acidic based on the manufacturing process and the utilized raw materials [9]. GWW is Energies 2021, 14, 4936 greasy and fibrous containing bovine bone pieces and hairs, resulting2 in of 18high quantities of particulate organic matters [11,12]. The particulates mainly consist of animal crushed bones, skin, and hair, which is highly obnoxious [9]. The COD of GWW ranged from bones, skin, and9691.2 hair, to which23,016 ismg/L highly due obnoxious to the usage [9]. of The raw COD materials of GWW rich ranged in proteins, from lipids, and 9691.2 to 23,016carbohydrates. mg/L due The to the bovine usage hide of rawis soaked materials in a lime rich tank in proteins, at a pH lipids,exceeding and 12.0 for 10–12 carbohydrates.weeks, The resulting bovine hide in high is soaked residual in values a lime of tank calcium at a pHin the exceeding wastewater 12.0 streams for ranging 10–12 weeks,from resulting 3175.3 in highto 5210 residual mg/L valuesand alkaline of calcium pH of in 11.1–12.4. the wastewater Sodium streams hydroxide ranging is added during from 3175.3 tothe 5210 manufacturing mg/L and process alkaline resulting pH of 11.1–12.4. in alkalinity Sodium of 5432–6527 hydroxide mg isCaCO added3/L [3,5]. Sulfate 4−2 4 during the manufacturing(SO ) (1000–1496 process mg/L) resulting and NH in alkalinity–N (163.2–190 of 5432–6527 mg/L) are mg produced CaCO3/L in [ 3the,5]. GWW due to −2 Sulfate (SO4 the) (1000–1496ammonification mg/L) and and acidification NH4–N (163.2–190 processes mg/L) [3,6]. The are discharge produced of in such the wastewater GWW due tointo the ammonificationsewerage networks and or acidification water streams processes causes [3 severe,6]. The pollution discharge problems of such for drinking wastewater intowater sewerage [13–15]. networks This wastewater or water streamsshould causesbe treated severe prior pollution to discharging problems it into the for drinking waterenvironment [13–15]. due This wastewaterto its negative should impact be treated on the prior water to discharging streams [12,16,17]. it into However, the environmentsimultaneous due to its treatment negative impactand biofuels on the produc watertion streams from [GWW12,16,17 save]. However, energy and chemicals simultaneousand treatment produces and less biofuels excess production sludge [18]. from GWW save energy and chemicals and produces less excess sludge [18]. 2. Gelatin Compositions, Properties, Manufacturing Processes, Utilization, and 2. Gelatin Compositions,Applications Properties, Manufacturing Processes, Utilization, and Applications Gelatin is a slightly yellow, translucent, brittle solid matter, nearly tasteless, and Gelatin isodourless a slightly [7,18,19]. yellow, translucent,The gelatin brittleis mainly solid extracted matter, nearly from tasteless,the collagen and of animals’ odourless [7,18connective,19]. The gelatin tissue is(Figure mainly 1). extracted Collagen from represents the collagen 25–35% of animals’ of the total connective protein in the whole tissue (Figureanimal1). Collagen body. Gelatin represents is a 25–35%high molecular of the total weight protein protein in the composed whole animal of eighteen types of body. Gelatin is a high molecular weight protein composed of eighteen types of amino amino acids (Figure 1). Amino acids contain oxygen, carbon, nitrogen, and hydrogen, acids (Figure1). Amino acids contain oxygen, carbon, nitrogen, and hydrogen, forming forming proteins [20]. They contain an amino group (NH2) and a carboxyl group (COOH– proteins [20]. They contain an amino group (NH ) and a carboxyl group (COOH–). Gelatin ). Gelatin is composed of 98–99% protein2 and could be varied based on the source of the is composed of 98–99% protein and could be varied based on the source of the original original raw materials and manufacturing processing technique [8,21]. The amino acids of raw materials and manufacturing processing technique [8,21]. The amino acids of gelatin gelatin are 22% for glycine, 12% for proline, 12% for hydroxyproline, 10% for glutamic are 22% for glycine, 12% for proline, 12% for hydroxyproline, 10% for glutamic acid, 9% acid, 9% for alanine, 8% for arginine, 6% for aspartic acid, 4% for lysine, 4% for serine, 3% for alanine, 8% for arginine, 6% for aspartic acid, 4% for lysine, 4% for serine, 3% for for leucine, 2% for valine, 2% for phenylalanine, 2% for threonine, 1% for isoleucine, 1% leucine, 2% for valine, 2% for phenylalanine, 2% for threonine, 1% for isoleucine, 1% for for hydroxylysine, <1% for methionine, and histidine and <0.5% for tyrosine. hydroxylysine, <1% for methionine, and histidine and <0.5% for tyrosine. Figure 1.FigureGelatin 1. compositionGelatin composition and general and overviewgeneral overview of its production of its production process. process. The schematicThe diagram schematic (Figure diagram2) shows (Figure the steps 2) shows of the the manufacturing steps of the manufacturing processes of processes of gelatin from thegelatin animal’s from bonesthe animal’s and skin. bones Gelatin and isskin. mainly Gelatin derived is mainly from derived the skins from of pigs the skins of pigs and cattle. Theand raw cattle. skin The is dried, raw skin acidified is dried, followed acidified by alkalinefollowed processes by alkaline to extractprocesses the to extract the collagen [18]. The manufacturing processes of gelatin from animals are comprehensively discussed by [7]. Gelatin applications in the industries are presented in Figure3. Energies 2021, 14, x FOR PEER REVIEW 3 of 19 Energies 2021, 14, x FOR PEER REVIEW 3 of 19 Energies 2021, 14, 4936 collagen [18].