Current Organic Chemistry - Volume 20, Issue 26, 2016

This mini review focuses on the current developments in the field of dark fermentation technologies using wastewater as carbon and nutrient source in batch reactors. Besides, the major microbiota (pure, enriched mixed, co and mixed cultures) involved in the process have been emphasized. Additionally, problems associated with the lower production performances and the overcoming strategies applied to enhance the production rate (HPR) and yield (HY) bybio-augmentation, immobilization, enrichment technique and nano particles (NP) addition were also discussed. This mini review provides more insights about the recent developments in the dark fermentative hydrogen production (DHFP) process and their advantages in a brief manner. The perspective towards the development of sustainable society by using bioH2 technology is enlightened.

Fermentation has become a reliable, cost-competitive, feasible alternative for large-scale industrial production of many bulk and special organic acids. Electrodialysis with bipolar membranes (EDBM) technology was considered as a ‘‘green’’ process for organic acid separation from fermentation broth, which has distinct advantages over other electrolysis- based technologies. However, review on the new state on this field is limited. This paper provides an overview of recent progress in application of EDBM process for organic acid production from 2008 to the latest one, including EDBM process integration, application and maintenance. Especially, the influence of different operational factors on the performance of EDBM was systemically discussed. Furthermore, the gaps limiting large-scale field application of EDBM process were analyzed.

Large amount of sludge has been a serious problem due to its great environmental risk. Anaerobic digestion (AD) is a commonly used method to treat sludge. Timely review of research developments of sludge AD is needed to gain insight for its future research and industrial applications. This paper summarized the main research developments of sludge AD from 2012 to 2015. The research hotspots of sludge AD from 2012 to 2015 were divided into three parts: sludge pretreatments, sludge co-digestion with other substrates, and the fate of emerging contaminants during sludge AD. Publications on pretreatments have shown an increasing trend from 2012 to 2015. Physical, chemical, biological, and combined pretreatments could all improve sludge AD efficiency, and physical pretreatment was the most reported group, accounting for 45.9%. Removing extracellular polymer substances has been a new pretreatment method in the last four years. As for sludge co-digestion with other substrates, publications have increased by 112% from 2012 to 2015. Other organic waste was the most widely reported co-substrate, followed by biowaste, fat, oil and grease, and combined waste. All of these co-substrates could improve biogas (methane) production with suitable mixed ratio and organic load rate. As for the fate of emerging contaminants during sludge AD, pharmaceuticals have been the most researched group, which accounted for 52.7% of total publications. The removal efficiencies of various emerging contaminants had a great difference during sludge AD. Future perspectives of above three research hotspots were also discussed in details.

Sulfur compounds play a significant role in low treatment efficiency, production of corrosive gases and unpleasant odors during sludge anaerobic digestion, which limits its environment and economic benefits. Better understanding of sulfur transformations, inhibitions and inhibition control methods is deemed necessary for enhancing the wider application of sludge anaerobic digestion. This review presented a detailed summary of research on the pathways and properties of sulfur transformations (dissimilation, assimilation and desulfurization), sulfur inhibitors (e.g. sulfide and sulfate reducing bacteria) and their inhibition mechanisms in sludge anaerobic digestion. The effects and mechanisms of various physical (e.g. thermal and ultrasound pretreatments), chemical (e.g. oxidative pretreatments and adding metal salts) and biological control methods (microaerobic desulfuration) on sulfur inhibition were also evaluated in sludge anaerobic digestion. Besides, a proper method was proposed to control sulfur inhibition in sludge anaerobic digestion according to existing studies.

Electrodeionization (EDI) process is a relatively new process applied in environmental engineering, which combines electrodialysis and conventional ion exchange. The EDI process has obvious advantages compared with the traditional deionization equipments based on the chemical regeneration. This review first time evaluated the importance of EDI process for bioproduct recovery (organic acid recovery, bio-methane concentration and bioelectricity production) and CO2 capture and storage. It highlighted not only the principal mechanisms but also the recent application development. Meanwhile, gaps which limited the large-scale field application of EDI process were also discussed in this paper.

Lignocellulosic biomass, as a sustainable bioenergy source, can be used to supplement fossil fuel. However, the utilization of lignocellulosic biomass for energy production has not been widely applied because of the complicated and stable structure of plant cell wall. Hydrothermal pretreatment of lignocellulosic biomass is an efficient method to disrupt lignin and hemicellulose and expose cellulose. Nowadays, many literatures demonstrated the mechanisms of hydrothermal pretreatment and the change of lignocellulosic biomass (including cellulose, hemicellulose and lignin) during hydrothermal pretreatment. Up to now, however, there is no review on this field. This paper reviews the research effort on hydrothermal pretreatment of lignocellulosic biomass and explains how the hydrothermal pretreatment affects the properties of lignocellulosic biomass. This review puts emphasis on the detailed changes of cellulose, hemicellulose and lignin during hydrothermal pretreatment. In addition, the future research directions are also prospected.

This review indicates that although anaerobic treatment has the advantage of methane energy production, release of effluent dissolved methane into the atmosphere results in unwanted greenhouse gas (GHG) emissions. Reported concentrations of dissolved methane are 8 – 40 mg/L, accounting for about half of the total methane production from the treatment of low strength wastewaters. The dissolved fraction of the methane produced is affected by several factors such as reactor type, influent organic concentration, hydraulic retention time (HRT), solids retention time (SRT), temperature, influent sulfate concentration, and reactor mixing conditions. In addition, oversaturation with methane is typical for reactors without membranes or when operated at short HRT. If dissolved methane is not recovered, GHG emissions from anaerobic treatment could be much greater than that from conventional activated sludge treatment. The recovery of dissolved methane is essential in order to enhance energy production as well as to reduce GHG emissions when anaerobically treating for low strength wastewater.

Artificial enzymes have emerged as cheaper, more robust and chemically malleable alternatives for natural enzymes in the chemical reactions. The importance of cyclodextrin nanoreactors with the hydrophilic exterior surface and the hydrophobic interior core as host structures in artificial enzymes designing has attracted special attention over the last years. The aim of the present paper is to review three different categories of cyclodextrin- based artificial enzymes including metal free cyclodextrin-based artificial enzymes, cyclodextrin-based artificial metalloenzymes and cyclodextrin-based artificial enzymes with computational design, focusing on their rate acceleration factor. Each of the three categories mimics enzymes such as oxidase, reductase, dehydrogenase, esterase, aminotransferase, glycosidase, protease, nuclease etc., which are accompanied by the comprehensive information about the relationship between their structure and activity.