Romeela Mohee

Influence of carbon-to-nitrogen ratio on the mixed-acid fermentation of wastewater sludge and pretreated bagasse.

In mixed-acid fermentation, carbon and nitrogen are critical nutrients for cell synthesis, growth, and metabolism. To study the effect of C/N ratio on the yield of carboxylic acids, wastewater sludge was co-digested with pretreated bagasse; the amount of sludge was varied from 0% to 100% (dry weight basis). Fermentation was performed at 55°C at a solids concentration of 50 g dry solids/L, and Iodoform was used to inhibit methane formation. It was observed that C/N ratio significantly affects yield, especially at extreme ratios. The highest carboxylic acid yield (0.36 g acids/g VS fed) was obtained for C/N ratios ranging from 13 to 25 g C/g N. C/N ratio also affected the composition profile of carboxylic acids. In all mixtures, acetic acid was the major fraction, followed by butyric acid. However, i-butyric, valeric acid, and i-valeric acid increased with increasing sludge content, which likely resulted from protein degradation.

Effects of pre-treatment technologies on dark fermentative biohydrogen production: A review

Biohydrogen production from dark fermentation of lignocellulosic materials represents a huge potential in terms of renewable energy exploitation. However, the low hydrogen yield is currently hindering its development on industrial scale. This study reviewed various technologies that have been investigated for enhancing dark fermentative biohydrogen production. The pre-treatment technologies can be classified based on their applications as inoculum or substrates pre-treatment or they can be categorised into physical, chemical, physicochemical and biological based on the techniques used. From the different technologies reviewed, heat and acid pre-treatments are the most commonly studied technologies for both substrates and inoculum pre-treatment. Nevertheless, these two technologies need not necessarily be the most suitable since across different studies, a wide array of other emerging techniques as well as combined technologies have yielded positive findings. To date, there exists no perfect technology for either inoculum or substrate pre-treatment. Although the aim of inoculum pre-treatment is to suppress H2-consumers and enrich H2-producers, many sporulating H2-consumers survive the pre-treatment while some non-spore H2-producers are inhibited. Besides, several inoculum pre-treatment techniques are not effective in the long run and repeated pre-treatment may be required for continuous suppression of H2-consumers and sustained biohydrogen production. Furthermore, many technologies employed for substrates pre-treatment may yield inhibitory compounds that can eventually decrease biohydrogen production. Consequently, much research needs to be done to find out the best technology for both substrates and inoculum pre-treatment while also taking into consideration the energetic, economic and technical feasibility of implementing such a process on an industrial scale.

Assessing the effect of biodegradable and degradable plastics on the composting of green wastes and compost quality

An assessment of the effect of the composting potential of Mater-Bi biodegradable plastic with green wastes, noted by GBIO, and degradable plastic (PDQ-H additive) with green wastes, noted by GDEG, was carried out in a lagged two-compartment compost reactor. The composting time was determined until constant mass of the composting substrates was reached. The green wastes composting process was used as control (G). After one week of composting, the biodegradable plastics disappeared completely, while 2% of the original degradable plastic still remained after about 8 weeks of composting. A net reduction in volatile solids contents of 61.8%, 56.5% and 53.2% were obtained for G, GBIO and GDEG, respectively. Compost quality was assessed in terms of nitrogen, potassium and phosphorus contents, which were found to be highest for GBIO compost. From the phytotoxicity test, it has been observed that a diluted extract of GBIO compost has produced the longest length of radicle. From the respiration test, no significant difference in the amount of carbon dioxide released by the composting of GDEG and G was observed. This study showed that the quality of the compost is not affected by the presence of the biodegradable and degradable plastics in the raw materials.

Current status of solid waste management in small island developing states: A review

This article reviews the current status of waste management in Small Island Developing States (SIDS) and the challenges that are faced in solid waste management. The waste generation rates of SIDS were compared within the three geographic regions namely Caribbean SIDS, Pacific SIDS and Atlantic, Indian Ocean, Mediterranean and South China (AIMS) SIDS and with countries of the Organisation for Economic Co-Operation and Development (OECD). Only Pacific SIDS had a waste generation rate less than 1kg/capita/day. The waste generation rates for the three SIDS regions averaged 1.29kg/capita/day while that for OECD countries was at a mean value of 1.35kg/capita/day. The waste compositions in the different SIDS regions were almost similar owing to comparable consumption patterns while these differed to a large extent with wastes generated in OECD countries. In SIDS, the major fraction of MSW comprised of organics (44%) followed by recyclables namely paper, plastics, glass and metals (total: 43%). In contrast, MSW in OECD countries consisted mainly of recyclables (43%) followed by organics (37%). This article also reviewed the other functional elements of the waste management systems in SIDS. Several shortcomings were noted in the process of waste collection, transfer and transport namely the fact of having outdated collection vehicles and narrow roads which are inaccessible. Among the waste management practices in SIDS, waste disposal via landfilling, illegal dumping and backyard burning were favoured most of the time at the expense of sustainable waste treatment technologies such as composting, anaerobic digestion and recycling.

ASSESSING THE RECOVERY POTENTIAL OF SOLID WASTE IN MAURITIUS

Abstract A study was initiated to assess the recovery potential of solid waste in Mauritius. The solid waste generated in a residential area has been quantified and characterized using direct weighing, physical testing and truckload sampling methods. Data on quantities of solid waste and waste composition has been collected for six months to assess for seasonal variation in solid waste generation rates. The current situation concerning resource recovery and disposal of solid waste in Mauritius is also described. Alternative decisions of solid waste appropriate with local conditions are discussed. It has been seen that the average solid waste generation rate is around 1.3 kg/capita per day and that wastes generated in winter were significantly different from wastes generated in the summer seasons. The composition (on a weight basis) of the solid wastes sampled was as follows: food wastes 25%, yard waste 43%, plastics 13%, paper 12%, textiles 3%, metals 1% indicating a high amount of organic matter. Vegetable and food wastes from the kitchen and yard wastes accounted for more than 60% of the waste stream. The moisture content was around 48% and the calorific value of the mixed wastes around 18 800 kJ/kg on a dry weight basis. The nature of the wastes indicate that amongst the recovery options, composting at household level would be most appropriate as it would divert more than 60% of the wastes from the traditional waste stream and provide households with compost which could be used to enrich soils in the kitchen gardens.

Effect of thermochemical pretreatment on sewage sludge and its impact on carboxylic acids production.

This paper investigates the potential of converting sewage sludge into a useful product, namely carboxylic acids. To potentially enhance acid yields, the effect of pretreatment using 0.3 g lime/g dry biomass and water at 100 degrees C for 10-240 min was studied. The pretreated sludges were anaerobically fermented to mixed-acids using a mixed culture of microorganisms; methanogens were suppressed using iodoform. Batch fermentations were performed at 55 degrees C using ammonium bicarbonate buffer. The first batch experiments compared treated and untreated sludge as the only substrate. The second batch experiments used a mixture of sludge plus lime-treated bagasse (20:80 by weight). Analysis of liquor shows that the pretreatment were effective in solubilizing constituent compounds of sewage sludge. Nitrogen content and carboxylic acids increased with increasing pretreatment time. However, the soluble sugars peaked at 60 min, and then decreased with longer pretreatment time, showing that the solubilised sugars were undergoing intermolecular reactions, such as Maillard reactions. Fermentation experiments were a good indicator of the biodegradability of the pretreated sludges. Results clearly showed that lime-treating sludge, using even the minimum pretreatment time (10 min), negatively impacted acid production. The likely causes of this observation are attributed to the production of recalcitrant complexes and toxic compounds. Batch fermentation of untreated sludge yielded 0.34 g total acids/g VS fed, whereas sludge with 240-min lime pretreatment yielded only 0.20 g total acids/g VS fed. Co-fermentation of untreated sludge with pretreated bagasse gave a yield of 0.23 g total acids/g VS fed.

Windrow co-composting of shredded office paper and Broiler Litter

The co-composting of shredded waste office paper with Broiler Litter (BL) in windrows was analysed in this study. Two compost mixes were monitored for five weeks; Mix 1 comprised 322kg BL, 117 kg shredded paper and 310L water and Mix 2 consisted of 112 kg BL, 265 kg shredded paper and 290 L water. The initial wet moisture content, initial porosity and initial wet bulk density for Mix 1 were 54.6%, 74.7% and 337kg/m?, respectively. The respective parameters for Mix 2 were 48.6%, 87.7% and 185 kg/m?. The initial C:N ratio was kept at 20.8 in both mixes. Peak temperatures recorded for Mix 1 and Mix 2 at day 5 were 71.4?C and 62.7?C, respectively. Temperatures remained above 60?C for more than 10 days in both windrows. The pH for both mixes varied between 7.2 and 8.8. An increase in wet bulk density of 47.6% for Mix 1 and 150% for Mix 2 was obtained. The net decrease in Volatile Solids (VS) was of 57.1% (Mix 1) and 56.3% (Mix 2) at the end of week 5. The respiration rate peaked at 33.7 mg CO2.C/day.gVS on day 3 for Mix 1 and decreased to 0.98 mg CO2.C/day.gVS on day 37. The concentrations of lead, cadmium, total chromium and zinc were 612 mg/kg, 60.8 mg/kg 103.2 mg/kg and 5760 mg/kg, respectively, in the final compost of Mix 1. NPK content of the final compost from Mix 1 was 5-5-10 (dry matter basis) with a level of phosphorous of 20,817 ppm.

Spectroscopic, thermogravimetric and structural characterization analyses for comparing Municipal Solid Waste composts and vermicomposts stability and maturity

This is the first-ever study of its kind for an extensive assessment and comparison of maturity indexes between compost and vermicompost that have been derived from Municipal Solid Waste (MSW). The spectroscopic (Fourier transform infrared spectroscopy: FT-IR), thermogravimetric analysis (TG), differential scanning calorimetry (DSC) and structural characterization (scanning electron microscope: SEM) were recorded. FT-IR spectra showed an increase in conversion of polysaccharides species and aliphatic methylene groups in vermicompost compared to compost as depicted from the variation of the intensity of the peaks. TG curves of final vermicompost showed a much lower mass loss when compared to compost, indicating higher stability in feedstock. SEM micrographs of the vermicompost reflected strong fragmentation of material than composts which revealed the extent of intra-structural degradation of MSW. These findings elucidate on a clear comparison between composts and vermicomposts in terms of maturity indexes for soil enhancement and in agriculture as organic fertilizer.

Life cycle analysis of compost incorporated sugarcane bioenergy systems in Mauritius.

Abstract Life cycle analysis has been used to compare the environmental performance of different sugarcane bioenergy systems. Environmental performance indicators such as resource consumption, chemical stressors and ecological health are used to analyse the trade-off between options. The reference fuel chain is based on current practices in Mauritius whereby bagasse in excess of sugar factory requirements is used to generate electricity for the grid. An alternative option uses the excess bagasse and factory filter cake to produce compost which when applied to the sugarcane plantations increases cane yield by up to 30% but at the expense of surplus electricity production. A third option combines improvements in steam management with composting of bagasse/filter cake. Results obtained from the comparative analysis show that it is possible to improve both the production of raw sugar (by 30%) and surplus electricity (by 190%) while reducing environmental stress as measured by the predefined eco-efficiency indicators.

Promising Unconventional Pretreatments for Lignocellulosic Biomass

This article has been retracted.