Biofuels are viewed as promising alternatives to conventional fossil fuels because they have the potential to eliminate major environmental problems created by fossil fuels. Among the still developing biofuel technologies, biodiesel production from algae offers a greater prospect for large-scale practical use, as algae are capable of producing much more yield than other biofuels. While research on algae-based biofuel is still in its developing stage, extensive work on laboratory- and pilot-scale algae harvesting systems with promising prospects has been reported. This paper presented a discussion of the literature review on recent advances in algae separation, harvesting and drying for biofuel production. The review and discussion focus on destabilization of algae, algae harvesting technologies and algae drying processes. Challenges and prospects of algae harvesting are also outlined.
Aerobic granulation was developed in overcoming the problem of biomass washout often encountered in activated sludge processes. The novel approach to developing fluffy biosolids into dense and compact granules offers a new dimension for wastewater treatment. Compared with conventional biological flocs, aerobic granules are characterized by well-defined shape and compact buildup, superior biomass retention, enhanced microbial functions, and resilient to toxicity and shock loading. This review provides an up-to-date account on development in aerobic granulation and its applications. Granule characterization, factors affecting granulation, and response of granules to various environmental and operating conditions are discussed. Maintaining granule of adequate structural stability is one of the main challenges for practical applications of aerobic granulation. This paper also reviews recent advances in addressing granule stability and storage for use as inoculums, and as biomass supplement to enhance treatment efficiency. Challenges and future work of aerobic granulation are also outlined.
Biohydrogen is regarded as an attractive future clean energy carrier due to its high energy content and environmental-friendly conversion. It has the potential for renewable biofuel to replace current hydrogen production which rely heavily on fossil fuels. While biohydrogen production is still in the early stage of development, there have been a variety of laboratory- and pilot-scale systems developed with promising potential. This work presents a review of advances in bioreactor and bioprocess design for biohydrogen production. The state-of-the art of biohydrogen production is discussed emphasizing on production pathways, factors affecting biohydrogen production, as well as bioreactor configuration and operation. Challenges and prospects of biohydrogen production are also outlined.
Biological removal of carbon, nitrogen and sulfur is drawing increasing research interest in search for an efficient and cost-effective wastewater treatment. While extensive work on separate removal of nitrogen and sulfur is well documented, investigation on simultaneous denitrifying sulfide removal has only been reported recently. Most of the work on denitrifying sulfide removal has been focusing on bioreactor performance, loading and operating conditions. Nonetheless, underlying principles elucidating the biochemical reactions and the mechanisms of the microbial degradation are yet to be established. In addition, unstable denitrifying sulfide removal which is a major operating problem that hinders practical application of the process, is yet to be resolved. This paper provides a review on the state-of-the-art development of simultaneous biological removal of sulfur, nitrogen and carbon. Research on bioreactor operation and performance, reactor configurations, mechanisms and modeling work including the use of mass balance analysis and artificial neural networks is delineated. An in-depth discussion on the microbial community and functional consortium is also provided. Challenges and future work on simultaneous biological removal of nitrogen-sulfur-carbon are also outlined.
This study presents an examination on the correlation of sonication operating condition, sludge property, formation and behaviour of cavitation bubbles in sludge disruption under low-frequency ultrasound sonication. The influence of sonication time, sonication density, type of sludge and solids content on the disruption was evaluated. The most vigorous particle disruption was achieved in the initial period of sonication, which subsided subsequently. The explosive effect was likely due to the rapid cavitation arising from powerful transient bubbles generated in fractions of microseconds. A rating for the type of sludge was derived based on the finding that particles in secondary sludge were more readily disrupted than both primary sludge and mixed sludge. While sonication density exhibited the most significant role in cavitation bubble formation and behaviour, particle disruption could be optimised for energy input by sonicating at higher sonication density and shorter sonication time. Based on theoretical consideration, it was deduced that within an optimum sludge solids content ranging between 2.3% and 3.2%, superior particle disruption could be accomplished within a minute for secondary sludge sonicated at a density of 0.52 W/mL. Useful guidelines for sonication system installation, equipment protection and process reliability could be established from knowledge derived from a good understanding on the influence of solids content on sludge sonication.
Conventional aerobic and low-rate anaerobic processes such as pond and open-tank systems have been widely used in wastewater treatment. In order to improve treatment efficacy and to avoid greenhouse gas emissions, conventional treatment can be upgraded to a high performance anaerobic granular-sludge system. The anaerobic granular-sludge systems are designed to capture the biogas produced, rendering a potential for claims of carbon credits under the Kyoto Protocol for reducing emissions of greenhouse gases. Certified Emission Reductions (CERs) would be issued, which can be exchanged between businesses or bought and sold in international markets at the prevailing market prices. As the advanced anaerobic granular systems are capable of handling high organic loadings concomitant with high strength wastewater and short hydraulic retention time, they render more carbon credits than other conventional anaerobic systems. In addition to efficient waste degradation, the carbon credits can be used to generate revenue and to finance the project. This paper presents a scenario on emission avoidance based on a methane recovery and utilization project. An example analysis on emission reduction and an overview of the global emission market are also outlined.
Safe disposal of effluent from palm oil production poses an environmental concern. The highly polluting effluent is customarily treated by unsustainable open ponds with low efficiency, direct emissions, and massive land use. This study looks into an application of integrated anaerobic/oxic/oxic scheme for treatment of high strength palm oil mill effluent. The anaerobic reactors functioned as a prime degrader that removed up to 97.5% of the chemical oxygen demand (COD), while the aerobic reactors played a role of an effluent polisher that further reduced the COD. Their complementing roles resulted in a remarkable removal of 99.7%. Assessment of emission mitigation and biogas energy revealed that yearly energy of 53.2 TJ, emissions reduction of 239,237 tCO2 and revenue of USD 1.40 millions can be generated out of electricity generation and heating. The integrated scheme provides a viable and sustainable treatment of the high strength palm oil mill effluent.
Microbial fermentation of organic matter under anaerobic conditions is currently the prominent pathway for biohydrogen production. Organic matter present in waste residues is regarded as an economic feedstock for biohydrogen production by dark and photo fermentative bacteria. Agricultural residues, fruit wastes, vegetable wastes, industrial wastewaters, and other livestock residues are some of the organic wastes most commonly used for biohydrogen production due to their higher organic content and biodegradability. Appropriate pretreatments are required to enhance the performance of biohydrogen from complex organic wastes. Biohydrogen production could also be enhanced by optimizing operation conditions and the addition of essential nutrients and nanoparticles. This review describes the pathways of biohydrogen production, discusses the effect of organic waste sources used and microbes involved on biohydrogen production, along with addressing the key parameters, advantages, and difficulties in each biohydrogen production pathway.