Lactic acid production from Kraft waste-pretreated corn cobs in dairy wastewater using Lactobacillus plantarum ATCC 14917: process modelling and preliminary scale-up.

Abstract

Microbial conversion of lignocellulosic biomass into value-added bioproducts like lactic acid (LA) is sustainable yet resource-intensive, characterized by low yields and costly operations. This study focused on the development of lignocellulosic LA bioprocesses through the valorization of agricultural, Kraft and dairy industrial waste. These wastes are low-cost, sustainable and discarded in abundance during raw material processing. Two complete wastebased pretreatment strategies: (1) steam-assisted combined GLD and PWW (SGLD-PWW), and (2) microwave-assisted combined GLD and PWW (MGLD-PWW) were developed and optimized using Response Surface Methodology (RSM) to enhance sugar release from corn cob waste (CCW). The CCW is non-food based, rich in carbohydrates, and geographically widespread. Artificial Neural Network (ANN) models were developed to predict glucose responses using experimental data from the Kraft waste pretreatment, followed by sensitivity analysis and comparative assessment with a Generative Artificial Intelligence (GAI) model like ChatGPT. Following pretreatment optimization, the Kraft waste pretreated CCW and supplemented dairy wastewater-based simultaneous saccharification and fermentation process (sDWW-SSF) was modelled and optimized using the RSM for LA concentration and conversion. The logistic and modified Gompertz models assessed the Lactobacillus plantarum ATCC 14917 cell growth and LA production kinetics for the: (1) supplemented DWW under SSF-microaerophilic (sDWW-SSFmicroaerophilic), (2) supplemented DWW under SSF-anaerobic (sDWW-SSFanaerobic), and (3) De Man, Rogosa and Sharpe medium modified with SGLD-PWW pretreated CCW instead of pure glucose under SSF-microaerophilic (mMRS-SSFmicroaerophilic). Prior to scale-up, various buffer agents, pH changes, micronutrient supplementation and bioprocess types were evaluated for enhanced LA production and sugar utilization. Optimized conditions for LA production were assessed at 0.5 L with specific vii mixing criteria: constant impeller tip speed (Vtip) and constant power input per unit volume (P/V), guiding subsequent scale-up to 5 L with kinetic analysis. For the CCW pretreatment optimization, the SGLD-PWW (49.89% GLD, 118°C, 5 min) strategy resulted in a 32% and 40% higher reducing sugar and glucose yield, respectively, compared to the MGLD-PWW (48.70% GLD, 800 W, 9 min) strategy. The SGLD-PWW technology was thereafter selected for the SSF process optimization towards LA production. The developed steam- and microwave-assisted ANN models showed high coefficient of determination (R2 ) scores >0.95 for the observed and predicted glucose responses. Sensitivity analysis revealed high susceptibility to the stepwise variation in GLD concentration from 0% to 50% (>3.3-fold increase) and power intensity from 100 W to 900 W (>2.6-fold increase) in relation to its baseline value. Furthermore, the GAI model provided key insights that coincided with the study’s contextual interpretations. These models offer a promising avenue to expedite labour-intensive wet lab experiments and enhance lignocellulosic pretreatment. The optimized sDWW-SSF (25g/L CSL, 2 mL/L Tween 80 and 10% SL) process gave a LA concentration and conversion of 11.15±0.42 g/L and 18.90±0.75%, respectively. For the kinetic studies, the sDWW-SSFmicroaerophilic system observed slightly lower maximum specific growth rate (μmax) (0.35 h-1 ) and maximum potential LA concentration (Pm) (13.01 g/L g/L) values than the mMRS-SSFmicroaerophilic (μmax= 0.64 h-1 , Pm= 14.01 g/L), but higher values than sDWW-SSFanaerobic (μmax= 0.34 h-1 , Pm= 12.01 g/L). The negligible variations in the Pm values achieved for the sDWW-SSFmicroaerophilic system highlights its economic and resource-efficient attributes, mitigating reliance on complex media, freshwater and anaerobic conditions. The SSF with CaCO3 and MnO nanoparticle (sDWW-SSFCaCO3(30)+MnO, pH5.5) achieved 31.12 g/L LA concentration and up to 46.27% sugar utilization at flask-scale. This contributed to a 64.17% (>2.7-fold) increase in LA concentration when paralleled to the sDWW-SSF system Microbial conversion of lignocellulosic biomass into value-added bioproducts like lactic acid (LA) is sustainable yet resource-intensive, characterized by low yields and costly operations. This study focused on the development of lignocellulosic LA bioprocesses through the valorization of agricultural, Kraft and dairy industrial waste. These wastes are low-cost, sustainable and discarded in abundance during raw material processing. Two complete wastebased pretreatment strategies: (1) steam-assisted combined GLD and PWW (SGLD-PWW), and (2) microwave-assisted combined GLD and PWW (MGLD-PWW) were developed and optimized using Response Surface Methodology (RSM) to enhance sugar release from corn cob waste (CCW). The CCW is non-food based, rich in carbohydrates, and geographically widespread. Artificial Neural Network (ANN) models were developed to predict glucose responses using experimental data from the Kraft waste pretreatment, followed by sensitivity analysis and comparative assessment with a Generative Artificial Intelligence (GAI) model like ChatGPT. Following pretreatment optimization, the Kraft waste pretreated CCW and supplemented dairy wastewater-based simultaneous saccharification and fermentation process (sDWW-SSF) was modelled and optimized using the RSM for LA concentration and conversion. The logistic and modified Gompertz models assessed the Lactobacillus plantarum ATCC 14917 cell growth and LA production kinetics for the: (1) supplemented DWW under SSF-microaerophilic (sDWW-SSFmicroaerophilic), (2) supplemented DWW under SSF-anaerobic (sDWW-SSFanaerobic), and (3) De Man, Rogosa and Sharpe medium modified with SGLD-PWW pretreated CCW instead of pure glucose under SSF-microaerophilic (mMRS-SSFmicroaerophilic). Prior to scale-up, various buffer agents, pH changes, micronutrient supplementation and bioprocess types were evaluated for enhanced LA production and sugar utilization. Optimized conditions for LA production were assessed at 0.5 L with specific mixing criteria: constant impeller tip speed (Vtip) and constant power input per unit volume (P/V), guiding subsequent scale-up to 5 L with kinetic analysis. For the CCW pretreatment optimization, the SGLD-PWW (49.89% GLD, 118°C, 5 min) strategy resulted in a 32% and 40% higher reducing sugar and glucose yield, respectively, compared to the MGLD-PWW (48.70% GLD, 800 W, 9 min) strategy. The SGLD-PWW technology was thereafter selected for the SSF process optimization towards LA production. The developed steam- and microwave-assisted ANN models showed high coefficient of determination (R2 ) scores >0.95 for the observed and predicted glucose responses. Sensitivity analysis revealed high susceptibility to the stepwise variation in GLD concentration from 0% to 50% (>3.3-fold increase) and power intensity from 100 W to 900 W (>2.6-fold increase) in relation to its baseline value. Furthermore, the GAI model provided key insights that coincided with the study’s contextual interpretations. These models offer a promising avenue to expedite labour-intensive wet lab experiments and enhance lignocellulosic pretreatment. The optimized sDWW-SSF (25g/L CSL, 2 mL/L Tween 80 and 10% SL) process gave a LA concentration and conversion of 11.15±0.42 g/L and 18.90±0.75%, respectively. For the kinetic studies, the sDWW-SSFmicroaerophilic system observed slightly lower maximum specific growth rate (μmax) (0.35 h-1 ) and maximum potential LA concentration (Pm) (13.01 g/L g/L) values than the mMRS-SSFmicroaerophilic (μmax= 0.64 h-1 , Pm= 14.01 g/L), but higher values than sDWW-SSFanaerobic (μmax= 0.34 h-1 , Pm= 12.01 g/L). The negligible variations in the Pm values achieved for the sDWW-SSFmicroaerophilic system highlights its economic and resource-efficient attributes, mitigating reliance on complex media, freshwater and anaerobic conditions. The SSF with CaCO3 and MnO nanoparticle (sDWW-SSFCaCO3(30)+MnO, pH5.5) achieved 31.12 g/L LA concentration and up to 46.27% sugar utilization at flask-scale. This contributed to a 64.17% (>2.7-fold) increase in LA concentration when paralleled to the sDWW-SSF system. The 0.5 L bioreactor revealed 18.25% higher LA concentration and 40% reduced production time for constant P/V, conferring enhanced mixing efficiency in comparison to the constant Vtip. At 5 L scale with constant P/V, LA concentration peaked at 31.43 g/L with up to 43.55% sugar utilization, corresponding to 0.26 h-1 μmax and 35.11 g/L Pm. The major findings of this study underscore that leveraging waste residues from agricultural, Kraft, and dairy industries fosters interdisciplinary co-operation among these stakeholders for the comprehensive valorization of waste into high-value commodities. This strategy coincides with global sustainable development goals and effectively contributes to optimizing the food-energy-water (FEW) nexus. Thus, it reflects a tangible step towards achieving a circular bioeconomy and integrated framework for lignocellulosic bioprocesses, promoting environmentally friendly processes and economic viability.

Iqoqa.

Ukuguquka kokuncu okubonakala ngesibonakhulu sesiphehlimandla samakhafilithi elignini, ilignocelllulosic kokwemikhiqizo yokuphilayo okwengeziwe njenge-esidi yokusabisi, ilactic acid (LA) egcinekayo kodwa ibe inezinsizasidingo ezinkulu, ebonakala ngemiphumela ephansi nokusebenza okubizayo. Lolu cwaningo lugxile ekukhuleni kokwamakhafilithi ilignocellulosic, i-LA yokwenza umshanguzo wokuphilayo ngokuqinisekisa kwezolimo, ngokweKraft nemfucuza yezimboni zokusabisi. Le mfucuza eyenani eliphansi, egcinekayo nelahlwa ngobuningi ngoba ingasadingeki ngenkathi kunohlelomsebenzi lwesiqalisimkhiqizo. Amasu amabili aphelele ohlelokwelapha olwandulelayo olugxile emfucuzeni: (1) Okusizwa isitimu okwakuhlanganisa i-GLD ne-PWW (SGLD-PWW), kanye (2) nokusizwa yimayikhroweyvu okwakuhlanganisa i-GLD ne-PWW (MGLD-PWW) kwakhuliswa kwaba ngokweqophelo eliphezulu kusetshenziswa Indlelakwenza Yendawo Yempendulo, iResponse Surface Methodology (RSM) ukuthuthukisa ukuphuma kukashukela emfucuzeni yehleza lommbila, icorn cob waste (CCW). I-CCW igxile kokungekona ukudla, okunezikhuthazimandla eziningi, futhi okusabalele ezindaweni eziningi. Imifanekisomumo yoHleloxhumano Lwemizwa Lokuzakhela, i-Artificial Neural Network (ANN) yakhuliswa ukubikezela izimpendulo zikashukela kusetshenziswa imininingo esahlolwa esuka kuhlelokwelapha olwandulelayo lwemfucuza yeKraft, ilandelwa uhlaziyo olunokuzwela nokuhlola okuqhathanisayo, iComparative assessment ngesifanekisomumo seGenerative Artificial Intelligence (GAI) njenge-ChatGPT. Kulandelwa uhlelo lokwelapha olwandulelayo lweqophelo eliphezulu, imfucuza yeKraft yokwelapha okwandulelayo i-CCW nokugxile emanzinimfucuza yokusabisi okuchibiyelelwe ngaso leso sikhathi kwaboniswa uhlelokusebenza lokugaywa kwamakhabhohaydrethi abe ushukela, isaccharification nokubilisa, ifermentation (sDWW-SSF) kwaba ngokweqophelo eliphezulu kusetshenziswa i-RSM yenguquko nesilinganisobungako se-LA. Inqubokusebenza nemifanekisomumo kaGompertz yahlola ukukhula kwenhlayiya kweLactobacillus plantarum ATCC 14917 ne-LA yohlelobumbanozithako olukhiqiza: (1) i-DWW echitshiyelwe phansi kwe-SSF-microaerophilic (sDWW-SSFmicroaerophilic), (2) echitshiyelwe phansi kwe-DWW ephansi kwe-SSF-anaerobic (sDWW-SSFanaerobic), (3) neDe Man, iRogosa neSharpe eguqulwe ngokumaphakathi nge-SGLD-PWW ukukwelapha okwandulelayo nge-CCW esikhundleni sikashukela ocolekile phansi kwe-SSF-microaerophilic (mMRS-SSFmicroaerophilic). Ngaphambi kokukhula kwesilinganisozinga, iziguquli zokungaguquki ezahlukene, izinguquko zezingabumuncu, i-pH, ukuthasiselwa kwesondlamzimba esincu esibonakala ngesibonakhulu nezihlobo zokwenza umshanguzo ngokuphilayo kwahlolwa ukuze kwenziwe ngcono ukukhiqizwa kwe-LA nokusetshenziswa kukashukela. Izimo zeqophelo eliphezulu zokukhiqizwa kwe-LA kwahlolwa ngokwama-0.5 L ngendlelakuqoka exube ngokucacile: isivinini se-impeller tip esingaquki (Vtip) nobungako obungaguquki besilinganiso samandla angenayo (P/V), okuqondisa ukulandelana kwesilinganisozinga esikhula ngama-5 L ngohlaziyo lohlolobumbanozithako. Ngokweqophelo eliphezulu lokwelapha okwandulelayo lwe-CCW, lwamasu e-SGLD-PWW (49.89% GLD, 118°C, 5 min) lwaba nomphumela ongama- 32% nangama-40% aphezulu ehlisa ushukela nomphumela kashukela, iglukhosi, uma kuqhathaniswa namasu e-MGLD-PWW (48.70% GLD, 800 W, 9 min). Ubuchwepheshe be-SGLD-PWW emuva kwalokho kwaqokelwa ukusetshenzwa kweqophelo eliphezulu kwe-SSF mayelana nokukhiqizwa kwe-LA. Umusi owakhuliswa nemifanekisomumo ye-ANN yokusiza ngemayikhroweyvu yakhombisa ivariyebuli ephezulu yokunquma (R2) izibalo ezi- >0.95 yokuqaphiwe noma yezimpendulo zikashukela ezabikezelwa. Uhlaziyo olunokuzwela lwaveza ukuba sengcupheni okuphezulu ngokwehluka kwesigaba sesilinganisobungako se-GLD ukusuka ku-0% kuya kumaphesenti angama- 50% (>3.3-ukukhula kwenanisiqhathaniso) nomfutho wamandla ukusuka e-100 W kuya ema-900 W (>2.6-ukukhula kwenanisiqhathaniso) kuhlobana nenani lesisekelo esiphansi. Ngaphezu kwalokho, isifanekosomumo i-GAI sanikezela ngamehlokujula asemqoka enzeka ndawonye nezihumusho zengqikithi yocwaningo. Lezi zifanekisomumo zinika izindlela zokusheshisa amalingasenzo elabhorethri elingemsulwa yomsebenzi odinga amandla amakhulu nokukhulisa ukwelapha okuyisandulelo sokwamakhafilithi elignini, iignocellulosic. I-sDWW-SSF yeqophelo eliphezulu (25g/L CSL, 2 mL/L Iwele lama-80 nayi-10% SL) indlelakwenza yanikeza isilinganisobungako se-LA nenguquko ye-11.15±0.42 g/L ne-18.90±0.75%, ngokulandelana. Ngokocwaningo lohlolobumbanozithako, uhlelo lwe-tsDWW-SSFmicroaerophilic lwaqaphela izingabungako lokukhula elicacile lesilinganiso esiphezulu eliphansi kancane elingu-(μmax) (0.35 h-1) namandla ayisilinganiso esiphezulu sesilinganisobungako se-LA esinesilinganiso esingu-(Pm) (13.01 g/L g/L) kune-mMRS-SSFmicroaerophilic (μmax= 0.64 h-1, Pm= 14.01 g/L), kodwa isilinganiso esiphezulu kune-sDWW-SSFanaerobic (μmax= 0.34 h-1, Pm= 12.01 g/L). Izinguquko ezinganakiwe zesilinganiso esiku-Pm esazuzwa ohlelweni lwe-sDWW-SSFmicroaerophilic zagqamisa umnotho nezimo zaso zezinsizakusebenza ezanele, zinciphisa ukwethembela kwezokuxhumana ezingxube, amanzi ahlanzekile nezimo zokudinga umoyampilo. Inhlayiya ye-SSF ne-CaCO3 kanye ne-MnO ye-(sDWW-SSFCaCO3(30)+MnO, pH5.5) yazuza ngama- 31.12 g/L esilinganisobungako se-LA futhi kuze kube ngama- 46.27% okusetshenziswa kukashukela kusikali seflaski. Lokhu kwanikela ngamaphesenti angama-64.17% (>2.7-inanisiqhathaniso) kuyakhula kusilinganisobungako se-LA ngenkathi kunokuhambisana nezinhlelo ze-sDWW-SSF. Amalitha angu-0.5 L enguqulo yokuphilayo aveza amaphesenti angama-18.25% aphezulu esilinganisobungako se-LA namaphesenti angama-40% ehlisa isikhathi sokukhiqiza kwe-P/V okuyinhlalanjalo, ukunikezela ngokwenzangcono kokwenzeka kokuxuba kuqhathaniswa nokuyinhlalanjalo kwe-Vtip. Esikalini esingamalitha ayi- 5 L esinokuyinhlalanjalo kwe-P/V, isilinganisobungako se-LA sanyukela kuma-31.43 g/L kunamaphesenti angama-43.55% okusetshenziswa kukashukela, kunokuhlobana no- 0.26 h-1 μmax nama-35.11 g/L Pm. Okukhulu okwatholwa yilolu ucwaningo kwagcizelela ukungasebenzisi kahle izinsalela zemfucuza ezisuka kwezolimo, iKraft, nezimboni zokusabisi kwakhuthaza ukubambisana phakathi kwemikhakha eyahlukene ngenxa yesola, ivalorization ehlanganise konke phakathi kwalokhu bonke abathintekayo abahlanganisa konke okwesola, okwevalorization yemfucuza yezimpahla zenani eliphezulu. Leli lisu lihlangana nezinhloso zokuthuthukisa okusimamisekayo komhlaba lokho kwasebenza kakhulu ekutholeni okweqophelo eliphezulu lenexus yokudla-amandla-amanzi (FEW). Kanjalo, kwakhombisa izigaba eziphathekayo ezimayelana nokuzuza umnotho wokuphilayo okujikelezayo nohlaka olungxube lohlelokusebenza lokuphilayo lokwamakhafilithi elignini, ilignocellulosic, ukukhuthaza izinhlelokusebenza ezivumelana nendawo nokomnotho okusesimeni sokwenzeka.