Analysis of Biogas Production from Biomass Residue of Palm Oil Mills using an Anaerobic Batch Test

The Malaysian palm oil industry has grown rapidly due to Malaysia’s tropical weather and suitable terrain. Palm oil production is now categorized as the most significant agriculture-based industry in the country. Along with strong economic returns, the palm oil industry also generates an abundance of waste products, including empty fruit bunches (EFB) (23%), mesocarp fibre (12%), shells (5%) and palm oil mill effluent (POME) (60%) for every batch of fresh fruit bunches (FFB) processed in the mills. This study is meant to fill the gap from previous studies in terms of biogas productions from the POME or the combination of POME and EFB which normally been conducted under the thermophilic conditions. The appropriate mixture ratios between POME and EFB in anaerobic digestion will reduce time of treatment and space if been conducted in the low temperature (mesophilic conditions). Thus, this paper is focuses on the analysis of batch test design which consist of low temperature (mesophilic, 20-40 °C) conditions for evaluating the performance of biogas production from the combination of POME and EFB in anaerobic digestion. The aim was to determine the amount of biogas production based on different ratios of POME and EFB mixtures. Biogas 1, containing 160 mL of fresh POME mixed with 40 g of EFB, was shredded and blended with 1800 mL seed sludge. Biogas 2, containing 120 mL of fresh POME mixed with 80 g of EFB, was shredded and blended with 1800 mL seed sludge. Based on the analysis of the results, the total production of Biogas 1 was greater than that of Biogas 2. The findings also show that the ratio of POME and 20% EFB (Biogas 1) was more efficient in producing the biogas compared to the ratio POME and 40% EFB (Biogas 2) under the mesophilic conditions. Thus, the mesophilic conditions required energy saving and low-cost process, compared to the previous studies which used the high temperature (thermophilic, 41-122 °C) that definitely was costly and require more energy consumption. This study will serve as preliminary results for enhancing the treatment methods use in Malaysia and form the early basis for the development of a new technology incorporating a combination of POME and EFB.

Mechanisms of chromium(VI) removal from solution by zeolite and vermiculite modified with iron(II)

Mechanisms of Cr(VI) reduction by Fe(II) modified zeolite and vermiculite were evaluated. Adsorbents were treated with Fe(SO4).7H2O to saturate their exchange sites with Fe(II). Vermiculite (V-Fe) adsorbed more Fe(II) (21.8 mg g−1) than zeolite (Z-Fe) (15.1 mg g−1). Z-Fe and V-Fe were used to remove Cr(VI) from the solution by batch test to evaluate the effect of contact time and Cr(VI) initial concentration. Cr(VI) was 100% reduced to Cr(III) by Z-Fe and V-Fe from solution with 18 mg L−1 Cr(VI) in 1 minute. Considering that 3 moles Fe(II) are required to reduce 1 mole Cr(VI) (3Fe+2 + Cr+6 → 3Fe3+ + Cr+3), the iron content released from Z-Fe and V-Fe were sufficient to reduce 100% of Cr(VI) in solution by up to 46.8 mg L−1 Cr(VI), and about 90% (V-Fe) and 95% (Z-Fe) in solution with 95.3 mg L−1 Cr(VI). The assess of the Fe(II), Cr(III), Cr(VI), and K+ contents of the adsorbents and solutions after batch tests indicated that K+ ions from K₂Cr₂O₇ solution were the main cation adsorbed by Z-Fe, while vermiculite did not absorb any of these cations. The H+ of the acidic solution (pH around 5) may have been adsorbed by V-Fe. Therefore, the release of Fe(II) from Z-Fe and V-Fe involved cation exchange between, respectively, K+ and H+ ions from solution. The reduction of Cr(VI) by Fe(II) caused the precipitation of Cr(III) and Fe(III), and the decrease of pH of the solution to < 5. As acidity limits the precipitation of Cr(III) ions, they remained in solution and were not adsorbed by both adsorbents (since they prefer to adsorb K+ and H+). To avoid oxidation, Cr(III) can be removed by precipitation or adsorption by untreated minerals.

Mill Scale Addition to Reduce Hydrogen Sulfide Production in Anaerobic Digestion

Direct addition of sulfur-reducing agents during anaerobic digestion (AD) is very effective in controlling hydrogen sulfide (H2S) content in biogas, although one major problem is the high operational cost due to the large amount of chemicals used. The objective of this study was to remove H2S using a waste mill scale (MS) as a sulfur-reducing agent. To evaluate its feasibility, MS was added to AD fed with food waste (FW) at concentrations between 0 and 160 g MS/kg total chemical oxygen demand (TCOD) during the batch test, and the experimental results were compared to those of the batch test with the addition of iron chloride (FeCl3). Both FeCl3 and MS played an important role as electro-conductive materials in improving methane productivity by promoting direct interspecies electron transfer. An increase in H2S removal efficiency was observed with increases in both materials. In total, 30%, 60%, and 90% of H2S production based on the maximum sulfur in the form of H2S (control) was 3.7, 9.4, and 23.8 g FeCl3/kg TCOD and 13.3, 34.1, and 86.2 g MS/kg TCOD, respectively. This finding indicates that MS can be used as a sulfur-reducing agent substitute for H2S removal in AD fed with FW.

Experimental investigation on buffer/backfill materials for radioactive waste repository downward facing sorption additivity of cesium, strontium and cobalt with different concentrations

Buffer/backfill materials for radioactive waste disposal sites consist of pure bentonite or bentonite-rock mixtures. In this study, the batch test method was used to obtain the sorption characteristics of important radionuclides such as Cs, Sr and Co on buffer/backfill materials; i. e., mixing Wyoming MX-80 bentonite or local Taiwanese Zhi-Shin bentonite with possible host rock (argillite and granite) in different proportions (0∼100%). The distribution coefficients (Kd) for Cs, Sr and Co were obtained from the experiments. The distribution coefficient for the bentonite-rock mixtures were found, with more than 50% of mixing proportion of bentonite to argillite or granite, to have very similar values to that of pure bentonite. Furthermore, it was clearly found that the sorption of Cs, Sr and Co to bentonite-rock mixtures is decreased as ionic strength of the liquid phase is increased from 0.001M to 1M for NaCl solutions. According to the experimental results, in synthetic groundwater, it is quite convenient and helpful to assess the distribution coefficients (Kd) of Cs, Sr and Co for buffer/backfill materials using batch sorption experiments with bentonite-rock mixtures of fixed mixing proportions.

Batch test to evaluate microbial disinfectant decay and the onset of nitrification

A batch test procedure was investigated to provide insight into the microbial contribution to disinfectant decay in drinking water distribution systems using chloramines. A modified method for determining the critical threshold residual (CTR), the intersection point on a semi-log plot between first-order total chlorine fitted decay curves before and after the breakpoint, was developed. Unlike the CTR as originally defined, initial sample conditions were retained rather than artificially raising the monochloramine concentrations. The CTR calculated with this modified method can more easily be applied to distribution system scenarios. In addition, four types of decay curves were identified and could distinguish differences in the microbial contribution to disinfectant residual decay. This study revealed that chloramine decay batch tests should be evaluated based on decay curve type, decay rates, and the CTR value, in addition to the microbial decay factor, which has been used alone in previous studies. The batch test approach and evaluation criteria established here can be used to predict conditions favorable for rapid chloramine decay and nitrification, and that monitoring and control strategies should be implemented.

Cometabolic biodegradation of chlorinated ethenes with methanotrophs in anaerobic/aerobic simulated aquifer

Aim: This study explores anaerobic/aerobic biodegradation efficiencies of aerobic cometabolism with methanotrophs when contaminants trichloroethylene (TCE) and cis-1,2-dichloroethylene (cDCE) are present individually or in tandem. Methodology: Batch tests and an anaerobic/aerobic column system were used to simulate saturated, contaminated aquifers. A brown glass bottle with an effective volume of 44 m l-1 was prepared for the batch test. An integrated one-dimensional sequential anaerobic/aerobic column system was used to simulate the accumulative intermediates such as TCE, cDCE and VC caused by incomplete degradation of PCE during the upgradient anaerobic stage in the saturated aquifer. In the downgradient aquifer, aerobic cometabolism was employed to degrade the intermediates. Methanotrophs in the aerobic aquifer were inoculated to degrade the by-products of incomplete degradation of PCE by aerobic cometabolism. Results: In the batch test, biodegradation of TCE was significantly inhibited by cDCE. However, biodegradation of cDCE was not significantly inhibited by TCE. In the simulated aquifer test, aerobic cometabolism completely degraded intermediates (TCE, cDCE, and VC) produced by incomplete anaerobic degradation of tetrachloroethylene (PCE). The results showed that methane, a by-product of anaerobic reductive dechorination of PCE, was used as a primary substrate for aerobic degradation, at a utilization rate of almost 100%. Interpretation: Biodegradation of TCE was significantly inhibited by cDCE. Bioremediation should have sufficient oxygen and methane at aerobic stage to ensure that chlorinated ethenes fully mineralize.

Determinação do fator de retardamento da uranina em sedimentos quaternários do aquífero São Paulo

A aplicação de substâncias fluorescentes como traçadores hidrogeológicos pode fornecer informações relevantes acerca da dinâmica das águas subterrâneas. Para um melhor controle na aplicação dos traçadores in situ, é pertinente definir possíveis interações dessas substâncias nos solos e sedimentos através de experimentos de bancada, a fim de prever seu comportamento durante a injeção no aquífero. O objetivo do trabalho corresponde à quantificação da adsorção e determinação do fator de retardamento do traçador fluorescente uranina em sedimentos quaternários da porção rasa do aquífero São Paulo. Os coeficientes de partição água/sedimento para uranina foram obtidos por meio de ensaios do tipo batch-test. Os experimentos consistiram em misturar sedimento orgânico, argiloso e grosso (arenoso) com soluções contendo uranina em cinco concentrações iniciais (5, 10, 50, 100 e 150 µg/L) em água deionizada e água do aquífero. Etapas de agitação, repouso e centrifugação precederam as medições de fluorescência. Através do ajuste de isotermas lineares, os valores do coeficiente de partição e fator de retardamento calculados para o sedimento grosso foram, respectivamente: 2,60x10-3 L/g ± 0,22x10-3 e 1,51 ± 0,13 (água deionizada), e 1,80x10-3 L/g ± 0,12x10-3 e 1,35 ± 0,09 (água do aquífero). Para o sedimento orgânico e argiloso, a fluorescência aparente gerada pelas partículas em suspensão nas soluções contendo uranina se sobrepôs à fluorescência real do traçador, impossibilitando a aferição dos coeficientes de partição e dos fatores de retardamento. Em meio sólido poroso com alto conteúdo de matéria orgânica e argilominerais, a uranina exibe alta susceptibilidade aos fenômenos de sorção. Contudo, sua utilização é indicada para a aferição de propriedades hidráulicas em aquíferos francamente quartzosos, uma vez nestes sedimentos a uranina apresentou um baixo fator de retardamento.