Evaluation of Hydraulic Retention Time on Treatment of Coffee Processing Wastewater (CPWW) in EGSB Bioreactor
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sustainability Article Evaluation of Hydraulic Retention Time on Treatment of Coffee Processing Wastewater (CPWW) in EGSB Bioreactor Abumalé Cruz-Salomón 1,* ID , Edna Ríos-Valdovinos 1,*, Francisco Pola-Albores 2, Selene Lagunas-Rivera 3 ID , Rocío Meza-Gordillo 4 and Víctor M. Ruíz-Valdiviezo 4 1 Faculty of Engineering, University of Science and Arts of Chiapas, Libramiento Norte Poniente No. 1150, Lajas Maciel, Tuxtla Gutiérrez C.P. 29039, Mexico 2 Center for Research and Technological Development in Renewal Energies, University of Science and Arts of Chiapas, Libramiento Norte Poniente 1150, Lajas Maciel, Tuxtla Gutiérrez C.P. 29039, Mexico; [email protected] 3 Professor CONACYT, Department of Chemical and Biochemistry Engineering, National Institute of Technology of Mexico-Tuxtla Gutiérrez Institute of Technology, Carretera Panamericana Km 1080, Tuxtla Gutiérrez C.P. 29050, Mexico; [email protected] 4 Department of Chemical and Biochemistry Engineering, National Institute of Technology of Mexico-Tuxtla Gutiérrez Institute of Technology, Carretera Panamericana Km 1080, Tuxtla Gutiérrez C.P. 29050, Mexico; [email protected] (R.M.-G.); [email protected] (V.M.R.-V.) * Correspondence: [email protected] (A.C.-S.); [email protected] (E.R.-V.); Tel.: +52-961-617-0440 (ext. 4272) (A.C.-S. & E.R.-V.) Received: 11 December 2017; Accepted: 23 December 2017; Published: 30 December 2017 Abstract: The coffee processing agro-industry generates large quantities of wastewater requiring systematic treatment prior to disposal. For this reason, the aim of this study was to evaluate the hydraulic retention times (HRT) in treatment of coffee processing wastewater (CPWW) using a laboratory scale Expanded Granular Sludge Bed (EGSB) bioreactor at different HRT (3 to 9 days). The EGSB was evaluated in mesophilic condition (26 ± 2 ◦C) with an average pH of 7.5 ± 0.2 to determine the chemical oxygen demand (COD) removal efficiency. According to the results, the COD removal efficiency increases from 94 to 98% when the HRT increase from 3 to 9 days; the α factor remained stable (0.98) throughout the evolution of the bioreactor. The HRT´s between 7–9 days generated effluents capable to be dischargeable into water bodies with a permitted COD concentration according to World Health Organization (WHO) and Official Mexican Environmental Regulations permissible limits. Results evidenced that the HRT of 9 days was the one that greater COD removal generated, so the EGSB bioreactor can be a sustainable alternative to solve the environmental problems, compared to other conventional methods to CPWW treatment. Keywords: anaerobic EGSB reactor; coffee processing wastewater; HRT; chemical oxygen demand; wastewater treatment 1. Introduction Coffee, which belongs to the genus Coffea of rubiaceae family, is one of the most popular beverages consumed throughout the world. Mexico ranks ninth in the world in coffee production with 2.4 × 103 Ton year−1. Both varieties of coffee Arabica (Coffea arabica) and Robusta (Coffea canephora) are cultivated mainly in the hilly tracts of the Sierra Madre del Sur and Sierra Madre Oriental mountain, being the state of Chiapas is one of the major and famous coffee producing region within Mexico with a contribution of 36.9% (74,538 Ton year−1)[1,2]. Sustainability 2018, 10, 83; doi:10.3390/su10010083 www.mdpi.com/journal/sustainability Sustainability 2018, 10, 83 2 of 11 Sustainability 2018, 10, 83 2 of 11 ThisThis regionregion has a number of of small small-scale-scale coffee coffee processing processing industries industries situated situated along along the the banks banks of ofrivers rivers and/or and/or streams streams to reduce to reduce production production costs. costs. The coff Theee coffeeis processed is processed either by either wet byor dry wet method or dry method(Figure (Figure1). Wet1 ).method Wet method of processing of processing results results in a coffee in a coffee of superior of superior quality quality compared compared to the to thedry drymethod. method. Presently Presently in Mexico, in Mexico, small small-scale-scale industries industries use use the the wet wet method method to process to process around around 86– 86–90%90% of ofcoffee coffee [3]. [3 ]. FigureFigure 1.1. General diagramdiagram ofof thethe coffeecoffee processing.processing. ** CoffeeCoffee processingprocessing wastewater.wastewater. TheThe processprocess byby wetwet methodmethod beginsbegins byby bringingbringing thethe coffeecoffee cherriescherries toto aa reservoir.reservoir. FromFrom herehere onon thethe cherriescherries areare transportedtransported byby gravitygravity toto thethe de-pulpingde-pulping machines.machines. InIn Chiapas,Chiapas, thethe transporttransport toto thethe de-pulpingde-pulping machinesmachines isis broughtbrought forthforth byby waterwater andand gravity.gravity. InIn thethe de-pulpingde-pulping machines,machines, thethe cherriescherries areare de-pulpedde-pulped (process in in which which the the pulp pulp and and the the outer outer skin skin are areremoved) removed) and andselected selected based based on their on theirsize. size.Nevertheless, Nevertheless, a slimy a slimy layer layer around around the thecoffee coffee bean bean with with a avarying varying thickness thickness of of 0.5 0.5 to 2 mmmm remains,remains, whichwhich willwill bebe laterlater eliminatedeliminated inin thethe fermentation.fermentation. InIn thethe fermentation fermentation process, process, the grainsthe grains remain remain between between 12 and 3612 h, and depending 36 h, ondepending the temperature, on the altitude,temperature, the thickness altitude,of the the thickness mucilage of layer the andmuc theilage concentration layer and the of enzymes.concentration The mucilageof enzymes. layer The is fermentedmucilage layer through is fermented a combination through of microbiala combination activity. of microbial activity. TheThe processprocess isis finishedfinished afterafter thethe grainsgrains areare washedwashed toto eliminateeliminate thethe lastlast remnantsremnants ofof decomposeddecomposed mucilage.mucilage. Afterwards,Afterwards, thethe grainsgrains inin pergaminopergamino statestate areare dried.dried. TheThe wetwet methodmethod toto coffeecoffee processingprocessing producesproduces aa veryvery highhigh loadload ofof pollutedpolluted wastewaterwastewater (CPWW(CPWW isis obtainedobtained from from de-pulping, de-pulping, generated generated in the in pulpthe removalpulp removal process process of coffee of cherries, coffee whichcherries, represent which morerepresent than more 50% than of the 50% water of the used water in used the wholein the whole process process [4]; and [4]; ofand the of washingthe washing process process which which is generatedis generated after after the the fermentation fermentation of of the the coffee coffee bean bean [5 [5]);]); this this is is the the reason reason whywhy coffeecoffee processingprocessing industriesindustries areare oneone ofof thethe significantsignificant consumersconsumers ofof water.water. TheyThey produceproduce largelarge amountsamounts ofof wastewaterwastewater (between(between 8–10 8–10 L ofL CPWWof CPWW are generatedare generated for each for kilogrameach kilogram of coffee of produced). coffee produced). The CPWW The generated CPWW fromgenerated this agro-industry from this agro presents-industry an acidpresents pH (3–5); an acid additionally, pH (3–5 it); containsadditionally, high concentrationsit contains high of organicconcentrations matter (1185–32,459of organic matter mg L −(11851 as– COD,32,459 3450–12,100 mg L−1 as COD, mg L −34501 as– biochemical12,100 mg L− oxygen1 as biochemical demand −1 −1 −1 −1 (BODoxygen5), 7000–10,900demand (BOD mg5), L 7000as–10 total,900 suspended mg L as total solids suspended (TSS)), nutrients solids ( (4.4–70TSS)), nutrients mg L as (4.4 phosphorus,–70 mg L 37–279as phosphorus, mg L−1 as 37 nitrogen)–279 mg and L− suspended1 as nitrogen matter) and [6 –suspended8]. In addition matter to these [6–8]. compounds, In addition the to CPWW these containscompounds, other the chemicals CPWW contains such as phenolsother chemicals (10–2904.7 such mg as L phenols−1) and (10 tannins–2904.7 (0.05–23 mg L−1 mg) and L− tannins1) that are(0.05 converted–23 mg L− into1) that recalcitrant are converted compounds into recalcitrant [9–11]. Thus,compounds considering [9–11]. the Thus, volume considering generated the andvolume the generated and the pollutants released through the wastewater, the coffee processing agro-industry represents one of the main contributors to the severe water pollution problems (as presented in a Sustainability 2018, 10, 83 3 of 11 Sustainability 2018, 10, 83 3 of 11 pollutants released through the wastewater, the coffee processing agro-industry represents one of the conceptualmain contributors model toFigure the severe 2). Despite water pollutionthe severe problems pollution (as problems, presented init was a conceptual found that model none Figure of the2). coffeeDespite processing the severe agro pollution-industries problems, (small it was-scale) found have that any none effl ofuent the treatment coffee processing plants. agro-industriesThey directly discharge(small-scale) untreated have any colored effluent and treatment acidic effluent plants. into They the directly nearby discharge water bodies, untreated streams colored and open and acidic land [12]effluent. into the nearby water bodies, streams and open land [12]. Furthermore,Furthermore, in the the literature, literature, it it has has been been