Valorization of sewage sludge for volatile fatty acids production and role of microbiome on acidogenic fermentation

This work explored the production of volatile fatty acids (VFA) through the anaerobic digestion of sewage sludge (SS). The first experiment took place at batch scale to evaluate the combined effect of using a thermal pre-treatment (120 °C, 15 min) and different Substrate/Inoculum ratios (S/I) (1, 2, 4 and 6 g VS substrate/g VS inoculum) on the acidogenic potential of the SS. The results showed that the thermal pre-treatment influenced positively the degree of acidification of the SS at low S/I ratios, reaching maximum of 45%. Afterwards, a continuous lab-scale experiment, was set-up to study two ranges of organic loading rates (OLR): 1300-1600 mg COD L^-1 d^-1 and 2400-3500 mg COD L^-1 d^-1. The highest degree of acidification (22%) was achieved at the lowest OLR. Analysis of the microbial community in the reactor revealed that OTUs most abundant present genes related with amino acids and carbohydrates fermentation being crucial for VFA production.

Acidogenic Potential of Packaged Fruit Juices and its Effect on Plaque and Salivary pH

AIM

The aim of this study was to analyze the acidogenic potential of the various commercially available fruit juices and to evaluate the salivary and plaque pH changes before and after consumption of the fruit juices that were kept at various temperatures.

MATERIALS AND METHODS

Baseline plaque and salivary pH were measured for 30 volunteers, and the test was conducted for 4 consecutive days on which juices with a known pH was consumed, which were kept at varying temperatures. The resulting changes in the plaque and salivary pH were measured after 1, 5, 15, and 30 minutes of the consumption of the fruit juices using a portable standard digital pH meter.

RESULTS

Among the three juices compared, grape juice was found to be more acidic compared to the orange juice and pineapple juice. The pH fall was maximum after consumption of grape juice followed by orange and pineapple juice, respectively. The consumption of ice candy caused a greater fall in pH followed by the refrigerated juice and the juices that were kept at room temperature, respectively.

CONCLUSION

Parents are unaware of the harmful effects of endogenous acids in the fruit juices and their effect on the teeth. We, as primary dental care providers, should take initiatives to provide adequate knowledge and information regarding this new trend of consuming frozen fruit juices and must strongly discourage this form of consumption as a frequent habit.

CLINICAL SIGNIFICANCE

Though many presume that the readily available fruit juices are healthy, frequent consumption of these fruit juices causes acid dissolution of enamel as most of these juices have a pH below the critical level. Hence the present study was conducted to evaluate the erosive potential of the various commercial fruit juices. As with increased awareness by both the dentists and the parents, the problem of fruit-juice-induced tooth loss may be reduced.

HOW TO CITE THIS ARTICLE

Mehta LK, Hegde A, et al. Acidogenic Potential of Packaged Fruit Juices and its Effect on Plaque and Salivary pH. Int J Clin Pediatr Dent 2019;12(4):312-317.

Selective VFA production potential from organic waste streams: Assessing temperature and pH influence

This study explored the volatile fatty acid (VFA) production potential of seven waste streams from urban and agroindustrial sources. For that purpose, batch assays were performed under acidic (pH 5.5) and alkaline (pH 10) conditions at both mesophilic (35°C) and thermophilic (55°C) temperature. Overall, the VFA yield was influenced by temperature, and it was positively affected by pH, ranging between 220 and 677mgCODg^-1COD_fed for liquid waste streams and between 127 and 611mgCODg^-1COD_fed for solid waste streams and urban sludge. The highest VFA concentration and highest VFA/sCOD ratio was obtained during the organic fraction of municipal solid waste (OFMSW) fermentation, with 8,320mgCODL^-1 and 94% at alkaline pH and mesophilic temperature. The results of this study suggest that selective VFA production, i.e. via propionic, butyric and acetic acid production, might be feasible for scaling-up purposes with specific waste streams by adjusting the process parameters.

Hydrolytic and acidogenic fermentation potential of food waste with source segregated feces-without-urine as co-substrate

This study explored a new approach to enhance VFA productivity from anaerobic co-digestion of food-waste (FW) with source-segregated brown-water (BW) [feces-without-urine]. Effort was made to separate urine and BW from the source (using no-mix-toilet) mainly to expedite further treatment and resource-recovery. Effect of alkaline-pH [B] and acclimatized acidogenic inoculum [C] on acidification efficiency was investigated and compared with raw FW+BW co-digestion [A]. Batch-assay results indicated that VFA productivity persists for 144-h with about 615%, 522% and 376% increase in VFA-COD, respectively for 3-conditions [A-C]; which accounted for 70%, 49% and 58% of CODs input, respectively. High butyric-acid was observed in [A] and [C], followed by acetic, propionic-acids; whereas, abundant acetic-acid (86% of TVFA) was observed in [B], which are the most favorable-forms for methane production or other value-added-products. For 144-h of acidification, this study validated the feasibility of maximizing VFA-yield by 7-12 times compared to FW or BW as a sole-substrate.