This study evaluates the effects of the varying substrate to inoculum ratios (S:I) of 0.5, 1, 2, 3, 4, 5, and 6 (volatile solids/VS basis) on the kinetics of biogas production during batch mesophilic (35 ± 1 ℃) anaerobic digestion (AD) of simulated food waste (FW), using anaerobic digestate as the inoculum. Kinetic parameters during biogas production (scrubbed with NaOH solution) are predicted by the first-order and the modified Gompertz model. The observed average specific biogas yields are in descending order corresponding to the S:I ratios 1, 2, 4, 6, 3, 5, and 0.5, respectively, and the significant effect of the S:I ratio was observed. The tests with the S:I of 1 have the maximum average biogas production rates of 88.56 NmL/gVS.d, whereas tests with the S:I of 6 exhibited the lowest production rates (24.61 NmL/gVS.d). The maximum biogas yields, predicted by the first order and the modified Gompertz model, are 668.65 NmL/gVS (experimental 674.40 ± 29.10 NmL/gVS) and 653.17 NmL/gVS, respectively. The modified Gompertz model has been proven to be suitable in predicting biogas production from FW. VS removal efficiency is greater in higher S:I ratios, with a maximum of 78.80 % at the S:I ratio of 6, supported by the longer incubation time. Moreover, a significant effect of the S:I ratio is seen on kinetics and energy recovery from the AD of FW.
Leachate analysis is a vital aspect of landfill operation & management, but limited studies have been conducted in Nepal in this regard. The study focuses on the chemical assessment of leachate’s characteristics of 4 different landfill sites in Nepal in the year 2019 among which 3 are operational and 1 closed, and their variation due to age, functionality, seasons, and feeding amount and waste composition. The data of leachate samples at two months’ interval was collected and assembled into 4 seasons viz. pre-monsoon (Mar-May), monsoon (June-Aug.), post-monsoon (Sep-Nov), and winter seasons (Dec-Feb.) of Nepal using Principal Component Analysis. One-way ANOVA tool is used to analyze data acquired from laboratory. Gradual increase of pH from pre-monsoon to winter seasons and as per age was observed. Amongst metals and heavy metals, the concentration of Fe descended from pre-monsoon to winter. Other metals like Ni, Pb, and Zn were detected in functional, and intermediate aged landfills. For old LFS, the concentrations of Fe, Cu, Cr, Hg, Ni, Pb, Cd, and Zn were lower. H2S and NH3 were high in intermediate than in mature site without seasonal variation. The chemical assessment generates useful data to construct treatment plants.
Ponds in Kathmandu were constructed to feed the sub surface aquifers of stone spouts and dug wells at all seasons. The study focuses on how the ponds have been saved, reduced in size or completely lost. The causes behind the degradation of ponds are forces of intervention and disturbances that lead to the loss of the originality, quality and quantity of ponds throughout its timeline. Out of eight existing ponds in the study area, 10 samples were taken from eight different ponds for quality assessment. The historical significances and status, uses as of 2019 are tabulated based on field survey. The paper focuses on the study of pH, Total Solids, Electrical Conductivity, Ammonia, Nitrate, Phosphate, Ammonia, Dissolved Oxygen, Biological Oxygen Demand, Total Organic Matter, Chlorophyll, E. Coli, and dimensions of existing ponds. The physical, social stresses and lack of regular inspection of ponds have contributed to their degradation. However, the existing ponds require sustainable management. Proper safeguarding mechanism should be developed for the regular aeration of water in the ponds such as fountains so that the ponds have more dissolved oxygen eliminating faulty smell and control fish death.
During the monsoon of 2022, Kathmandu valley witnessed an unprecedented number of cholera cases in a brief period- on an epidemic scale. This event corresponded with a month-long stagnation of Municipal Solid Waste (MSW) in the streets of the valley after protests and blockades from the residents in Sisdole- the location of the only landfill serving the valley. This paper has entertained the correlation between the two entities and has scrutinized the idea. To add to the study, the trends re studied and evaluated. Observations and literature reviews suggest MSW making the situation of cholera worse if not causing it. This study has also provided suggestions for getting the situation better in the longer term using available literature and has laid the groundwork for further research regarding the relationship between the two to further understand their significance on one another.
The start-up of two-stage, semi-continuous mesophilic anaerobic digestion (TSAD) of food waste is stabilized by altering the hydraulic retention time (HRT) and organic-loading rate (OLR). The volumetric biogas yield and composition are studied at OLR (0.25–0.50 gVS/L/d) and HRT (10, 20, 40 days) initiating at OLR 0.25 g VS/L/d and HRT of 20 and 40 days for the respective reactors. Methane (CH4) from the first stage of the two-staged reactor decreased from 18.20% to 0.06%, fostering hydrogen production in 44 days when the HRT was reduced from 20 to 10 days and OLR increased from 0.25 gVS/L/d to 0.50 gVS/L/d. During the alarming volatile fatty acids (VFA)/alkalinity ratio of 0.76, feeding to the second-stage reactor was halted until pH was restored to 7.00. The restoration of methanogens was evident by an increase in methane from 39.15% to 67.48%. A stable TSAD system produced 22.32 ± 4.16 NmL/gVS and 161.02 ± 17.72 NmL/gVS of yield in respective reactors. Thus, TSAD paves the path for multiple biofuels, i.e., H2 and CH4.
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