The demand for an adoption of renewable resources rather than finitely available non renewable sources for industrial purposes are rising, with the growing environmental constraints. Polymers being one of the crucial part of almost all the industries, pioneer in the list of sources needed for various applications. This makes polymers that can be obtained from renewable sources being studied widely and are anticipated to make a revolution in the field of packaging industry, medical field, and automobile industry. Polylactic acid (PLA) is one among such biopolymers, which is an aliphatic polyester derived from lactic acid (2-hydroxypropionic acid), that find wide applications in food packaging industry, tissue scaffolding, and biomedical devices. This paper focuses on an in-depth review on polylactic acid, its structure, and various properties of PLA. The details of different polymer blends/composites based on PLA are also discussed here. The fields of applications, where PLA is being utilized and the future scopes of the polymer are also studied.
The anaerobic digestion of kitchen waste was studied in both batch and continuous modes. The effect of increasing loading rates on pollutant removal and biogas production was investigated for single-phase digestion and twophase digestion systems. The anaerobic biodegradability of the kitchen waste obtained from the batch study was 83.5%. Single-stage digestion of kitchen waste was subjected to varying organic loading rates (OLR) ranging from 1.5 kg volatile solids (VS) m -3 d -1 to 5.5 kg VS m -3 d -1 , with a common hydraulic retention time (HRT) of 15 d. The optimum performance of the system was observed at an OLR of 4.5 kg VS m -3 d -1 in terms of pollutant removal efficiency and biogas production. The removal rates for chemical oxygen demand (COD) and VS at this optimal OLR were 81% and 79%, respectively. Maximum production of the methane was 0.288 m 3 /kg of VS added. Beyond the optimal OLR, the volatile fatty acids concentration increased and reached its maximum value (9.2 g/L) at the higher loading rate tested (5.5 kg VS m -3 d -1 ). Anaerobic digestion of the kitchen waste was carried out in a two-stage reactor with different loading rates of 4, 6, and 8 kg VS m -3 d -1 . The retention time given to both hydrolysis and methanogenesis phases was 5 d, for a total HRT of 10 d. Best performances were observed in the third run with the OLR of 8 kg VS m -3 d -1 . High removal efficiencies for COD and VS were found as 92% and 94%, respectively. A total of 0.22 m 3 of methane was produced by 1 kg of VS added. Responses to the fluctuations in the loading rates were sudden and many times unfavourable in the singlestage system, while the fluctuations were suppressed or overcome at a faster rate in the two-stage reactor, without creating too many problems. Comparison of the overall performance showed that phase-separated digesters or the two-stage digesters may offer the best choice for high efficiency, concerning pollutant removal.Résumé : La digestion anaérobie des résidus domestiques a été examinée en mode continu et par lot. L'augmentation des taux de charges sur l'élimination des polluants et sur la production de biogaz a été examinée pour les systèmes de digestion à une et à deux phases. La biodégradabilité anaérobie des résidus domestiques a atteint 83,5 % dans l'étude par lot. La digestion en une phase des résidus domestiques a été mise à l'épreuve avec des taux variables de charges organiques (OLR) de 1,5 kg de solides volatils (VS)/m 3 par jour à 5,5 kg VS/m 3 par jour, avec un temps de rétention hydraulique (HRT) commun de 15 jours. Le rendement optimal du système en termes d'efficacité d'élimination des polluants et de production de des biogaz a été atteint à un OLR de 4,5 kg VS/m 3 par jour. Les taux d'élimination de la demande chimique en oxygène et de VS à cet ORL optimal étaient respectivement de 81 % et de 79 %. La production maximale de méthane a été de 0 288 m 3 /kg de VS ajouté. Au-delà de l'ORL optimal, la concentration en acides gras volatils a augmenté et a atteint sa valeur maximale (9,2 g/L) ...
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