Influence of wastewater treatment on sludge production and processing

The challenge of stricter wastewater standards is resulting in configuration changes to wastewater treatment. As facilities upgrade, the type of sludge produced is changing, with growing quantities of secondary and chemical sludge at the expense of primary sludge. It is already understood that secondary sludge is harder to treat than its primary equivalent; therefore, increasing the quantity of this type of sludge will have detrimental impacts downstream. As legislation tightens further, extended aeration times may be required during processing to remove more nutrients. Work has shown that extended aeration further exacerbates the treatability of secondary sludge. This paper explains how tightening wastewater legislation fundamentally alters the nature of the sludge produced, and how these alterations impact further processing, especially with respect to sludge production and type; sludge energy content; performance of anaerobic digestion and dewatering, and potential for thermal energy recovery.     

The biochemical relationships in anaerobic digestion after thermal hydrolysis at Davyhulme

The commissioning of the largest thermal hydrolysis plant in the world at Davyhulme, Manchester involved detailed analysis of the digestion process. The plant consists of eight digesters, 20 thermal hydrolysis reactors and a maximum throughput of 121 000 tDS/year. The plant was converted from conventional digestion with a loading rate of 1.25 kgVS/m³/day to digestion fed with thermally hydrolysed sludge with a loading rate of 4.16 kgVS/m³/day. At the start of the commissioning and ramp‐up of the loading rate, control actions were based on acid/alkalinity, pH and foaming; however, it was found that the methane concentration was the parameter that changed quickest during digester instability. The monitoring was changed during commissioning to use methane concentration as the primary control parameter. It was found that the rate of increased organic loading is dependent on the availability of seed biomass already acclimatised to thermally hydrolysed feed sludge and the presence of a high alkalinity buffer.     

高硫铝土矿粗粒径焙烧脱硫及其溶出性能

分别对盘磨(粒径830μm占75%)和球磨(粒径75μm占85%)的一水硬铝石型高硫铝土矿进行焙烧脱硫处理,并与原矿进行溶出对比试验研究。结果表明,在700℃焙烧30min后,盘磨矿与球磨矿的硫含量分别从2.33%降至0.68%与0.64%,可以满足氧化铝生产工艺要求。当溶出条件为苛碱浓度245g/L、溶出温度260℃、石灰添加量8%、溶出时间60min时,焙烧矿氧化铝的溶出率提高了3.0~4.5个百分点。     

微波消解-石墨炉原子吸收法测定纸巾纸中砷含量

建立了石墨炉原子吸收光谱法测定纸巾纸中砷含量的方法。采用微波消解技术处理样品,加入基体改进剂硝酸镍,应用石墨炉原子吸收光谱法测定砷。结果表明,测定一次回归方程为Y=0.0025X+0.0004,相关系数r=0.9996。检出限为0.12 ug/L,回收率为95.8%～100.3%,相对标准偏差为2.37%。该方法具有快速、准确、灵敏度高等优点,适用于纸巾纸中砷含量的检测。     

消化吸收流水线制造模式管理 有效提高车间软实力

在认真分析技术引进转让知识的基础上,消化吸收其本质精神,结合车间实际情况,抓住制约车间发展的主要矛盾,突破一点,依托精细化生产组织、流水线制造模式,有效提高车间软实力。     

Technoeconomic analysis of an integrated microalgae photobioreactor, biodiesel and biogas production facility

As fossil fuel prices increase and environmental concerns gain prominence, the development of alternative fuels from biomass has become more important. Biodiesel produced from microalgae is becoming an attractive alternative to share the role of petroleum. Currently it appears that the production of microalgal biodiesel is not economically viable in current environment because it costs more than conventional fuels. Therefore, a new concept is introduced in this article as an option to reduce the total production cost of microalgal biodiesel. The integration of biodiesel production system with methane production via anaerobic digestion is proved in improving the economics and sustainability of overall biodiesel stages. Anaerobic digestion of microalgae produces methane and further be converted to generate electricity. The generated electricity can surrogate the consumption of energy that require in microalgal cultivation, dewatering, extraction and transesterification process. From theoretical calculations, the electricity generated from methane is able to power all of the biodiesel production stages and will substantially reduce the cost of biodiesel production (33% reduction). The carbon emissions of biodiesel production systems are also reduced by approximately 75% when utilizing biogas electricity compared to when the electricity is otherwise purchased from the Victorian grid. The overall findings from this study indicate that the approach of digesting microalgal waste to produce biogas will make the production of biodiesel from algae more viable by reducing the overall cost of production per unit of biodiesel and hence enable biodiesel to be more competitive with existing fuels.     

Effect of particle size on biogas yield from sisal fibre waste

The degradation and biogas production potential of sisal fibre waste could be significantly increased by pre-treatment for reduction of particle size. Batch-wise anaerobic digestion of sisal fibre waste was carried out in 1-l digesters with fibre sizes ranging from 2 to 100 mm, at an ambient temperature of 33 °C. Sediment from a stabilisation pond at a sisal production plant was used as starter seed. Total fibre degradation increased from 31% to 70% for the 2 mm fibres, compared to untreated sisal fibres. Furthermore, the results confirmed that methane yield was inversely proportional to particle size. Methane yield increased by 23% when the fibres were cut to 2 mm size and was 0.22 m³ CH₄/kg volatile solids, compared to 0.18 m³ CH₄/kg volatile solids for untreated fibres. By anaerobic digestion and biogas production, the 148,000 tonne of waste sisal fibres generated annually in Tanzania could yield 22 million m³ of methane, and an additional 5 million m³ of methane if pre-treatment by size reduction to 2 mm was applied.     

Pilot-scale high solids thermophilic anaerobic digestion of municipal solid waste with an emphasis on nutrient requirements

A pilot study was conducted to assess the biodegradable organic fraction of municipal solid waste (BOF/MSW) as a substrate in a high-solids anaerobic digestion process. Results obtained indicate that a typical BOF/MSW in the United States is deficient in most macro and micro-nutrients required for robust and stable digestion. The BOF/MSW was supplemented with nutrient-rich organic wastes such as wastewater treatment plant sludges, dairy manure, and synthetic chemical solutions to correct nutritional deficiencies. The combined addition of wastewater treatment plant sludge and dairy manure to a typical BOF/MSW significantly elevated the gas production rate and enhanced the process stability. Microbial nutrient requirements are identified and nutrient concentrations for stable operation are quantified.     

Production of hydrogen in a granular sludge-based anaerobic continuous stirred tank reactor

An investigation on biohydrogen production was conducted in a granular sludge-based continuous stirred tank reactor (CSTR). The reactor performance was assessed at five different glucose concentrations of 2.5, 5, 10, 20 and 40 g/L and four hydraulic retention times (HRTs) of 0.25, 0.5, 1 and 2 h, resulting in the organic loading rates (OLRs) ranged between 2.5 and 20 g-glucose/L h. Carbon flow was traced by analyzing the composition of gaseous and soluble metabolites as well as the cell yield. Butyrate, acetate and ethanol were found to be the major soluble metabolite products in the biochemical synthesis of hydrogen. Carbon balance analysis showed that more than half of the glucose carbon was converted into unidentified soluble products at an OLR of 2.5 g-glucose/L h. It was found that high hydrogen yields corresponded to a sludge loading rate in between 0.6 and 0.8 g-glucose/g-VSS h. Substantial suppression in hydrogen yield was noted as the sludge loading rate fell beyond the optimum range. It is deduced that decreasing the sludge loading rate induced the metabolic shift of biochemical reactions at an OLR of 2.5 g-glucose/L h, which resulted in a substantial reduction in hydrogen yield to 0.36–0.41 mol-_H2${\mathrm{H}}_2$/mol-glucose. Optimal operation conditions for peak hydrogen yield (1.84 mol-_H2${\mathrm{H}}_2$/mol-glucose) and hydrogen production rate (3.26 L/L h) were achieved at an OLR of 20 g-glucose/L h, which corresponded to an HRT of 0.5 h and an influent glucose concentration of 10 g/L. Influence of HRT and substrate concentration on the reactor performance was interrelated and the adverse impact on hydrogen production was noted as substrate concentration was higher than 20 g/L or HRT was shorter than 0.5 h. The experimental study indicated that a higher OLR derived from appropriate HRTs and substrate concentrations was desirable for hydrogen production in such a granule-based CSTR.     

Improvement of biohydrogen production from brewery wastewater: Evaluation of inocula,support and reactor

This work explores the production of biohydrogen from brewery wastewater using as inoculum a culture produced by natural fermentation of synthetic wastewater and Klebsiella pneumoniae isolated from the environment. Klebsiella pneumoniae showed good performance as inoculum, as evaluated using assays of between 9 and 16 cycles, with durations of 12 and 24 h, carbohydrate concentrations from 2.79 to 7.22 g L⁻¹, and applied volumetric organic loads from 2.6 to 12.6 g carbohydrate L⁻¹ day⁻¹. The best results were achieved with applied volumetric organic loads of 12.6 g carbohydrate L⁻¹ day⁻¹ and cycle length of 12 h, resulting in mean volumetric productivity of 0.88 L H₂ L⁻¹ day⁻¹, maximum molar flow of 10.80 mmol H₂ h⁻¹, and mean yield of 0.70 mol H₂ mol⁻¹ glucose consumed. The biogas H₂ content was between 18 and 42%, while the mean organic compounds removal and carbohydrate conversion efficiencies were 23 and 81%, respectively. The inoculum produced by natural fermentation was not viable.