Biotechnology developments for the treatment of toxic and inhibitory wastewaters

The cost-effectiveness of biological processes has encouraged many researchers to consider biotreatment for the stabilization of toxic or recalcitrant wastewaters. However, to ensure adequate removal of trace contaminants and satisfactory performance with high strength inhibitory industrial wastewaters, conventional biotechnology is being re-evaluated. This review summarizes selected recent contributions to the development of appropriate biotechnology for toxic wastewater treatment. Microbiological constraints and potential solutions are examined. Assessments of conventional biological processes for contaminant control are reviewed, and several new developments in bioreactor design for inhibitory wastes are presented.     

Bacterial Oxidation of Refractory Sulfide Ores for Gold Recovery

Abstract

The microbiological leaching of refractory sulfide ores (pyrite, arsenopyrite) for recovery of gold is reviewed in this article. The underlying physiological, biochemical, and genetic fundamentals of the bacteria involved (Thiobacillus and Sulfolobus spp.) are complex and have yet to be elucidated in depth. The chemistry of acid and biological leaching of pyrite and arsenopyrite minerals is also complex, and many of the individual reactions are not known in detail. Bacterial leaching is discussed in relation to chemical speciation at acid pH values. Attempts to develop models for a better understanding of bioleaching processes are summarized. The importance of pH, redox potential, temperature, sulfur balance, and toxic metals is evaluated for optimizing conditions for bacterial activity. Gold is finely disseminated in refractory sulfide ores, thereby decreasing Au recoveries upon conventional cyanidation for gold dissolution. In the bioleaching process, bacteria remove the sulfide minerals by oxidative dissolution and thus expose Au to extraction with cyanide solution. Stirred tank reactors appear most suited for this biological leaching process. The overall oxidation of the sulfides is an important variable for gold recovery. Pilot- and commercial-scale bioleaching processes for gold-containing pyrite and arsenopyrite ores are reviewed. This application of mineral biotechnology competes favorably with pressure leaching and roasting processes, both of which are problematic and energy-intensive alternatives for pretreatment of auriferous pyrite/arsenopyrite ores.     

Microbial Transformations of Selenium and the Bioremediation of Seleniferous Environments

Selenium (Se) exists in many natural soil and water environments around the world, but anthropological activities such as irrigated agriculture on Se-laden soils has created many ecological problems with respect to this element. Seleniferous agricultural drainage water in California's San Joaquin Valley has been linked to the death and deformity of waterfowl. In the environment, microbial reduction, oxidation, methylation, and demethylation reactions predominantly control the oxidation state of Se and its subsequent behavior. In an effort to remediate these Se-contaminated environments a number of biological technologies have been investigated. Biological transformations of toxic Se oxyanions into less toxic or biologically unavailable forms, such as elemental Se or volatile Se compounds, has received much attention over the last decade. In this literature review, a major emphasis is placed on Se reduction and methylation/volatilization reactions because these processes are currently the most promising techniques being investigated for the bioremediation of seleniferous soil and water.     

Fungal laccases as tools for the synthesis of new hybrid molecules and biomaterials

Laccase is a ligninolytic enzyme widely distributed in wood-rotting fungi and which is also found in a variety of molds and insects as well as some plants and bacteria. Its biological roles range from depolmerization of lignin, coal and humic acids via the oxidation of various mono- and diaromatic structures, to polymerization reactions and pigment formation in microbial cells or spores. Apart from its action in catabolic, depolymerizing and polymerizing processes, laccases have also been shown to be powerful enzymes for coupling two different molecules to create new low-molecular-weight products in high yield. In addition to their homomolecular coupling capabilities, laccases are also able to couple a hydroxylated aromatic substrate with a nonlaccase substrate of variable structure to create new heteromolecular hybrid molecules. Thus, laccases are increasingly finding applications in biotechnology in the fields of environment-friendly synthesis of fine chemicals and for the gentle derivatization of biologically active compounds e.g., antibiotics, amino acids, antioxidants, and cytostatics. Finally, oligomerization and polymerization reactions can lead to new homo- or heteropolymers and biomaterials. These may be useful in a wide range of applications including the production of polymers with antioxidative properties, the copolymerizing of lignin components with low-molecular mass compounds, the coating of cellulosic cotton fibers or wool, the coloring of hair and leathers, or the cross-linking and oligomerization of peptides.     

PAH Phytoremediation: Rhizodegradation or Rhizoattenuation?

Dealing with soil contaminated with persistent organic pollutants (POP) is an increasing concern amplified by both regulatory constraints and the dramatic impact of human activities on the soil resource. The most used management options are treatments which totally eradicate the toxic compounds targeted. When possible, environmental-friendly processes should be used, and recent years have seen the emergence of green technologies using biological energies involving microorganisms (bioremediation) and plants (phytoremediation). Research has focused on phytoremediation and many have presented this technology as the process ideally combining efficiency, low cost and environmental acceptance. However, the applicability of phytoremediation on soils contaminated by bio-recalcitrant organic compounds, such as polycyclic aromatic hydrocarbons (PAH), has not yet proved as successful as expected. We propose here a review and discussion of the overall question of PAH status in soil and their potential for treatment. The limits and applicability of bioremediation technologies are discussed, and the specific beneficial effect of plants is objectively evaluated with a special interest to processes which lead to rhizoattenuation. Given the PAH high affinity to soil organic matter, availability is the main limitation to phytoremediation. In this context, bioavailability quantification remains an issue as well as the characterization of the recalcitrant fraction.     

Harnessing the power of enzymes for environmental stewardship

Enzymes are versatile catalysts with a growing number of applications in biotechnology. Their properties render them also attractive for waste/pollutant treatment processes and their use might be advantageous over conventional treatments. This review highlights enzymes that are suitable for waste treatment, with a focus on cell-free applications or processes with extracellular and immobilized enzymes. Biological wastes are treated with hydrolases, primarily to degrade biological polymers in a pre-treatment step. Oxidoreductases and lyases are used to biotransform specific pollutants of various nature. Examples from pulp and paper, textile, food and beverage as well as water and chemical industries illustrate the state of the art of enzymatic pollution treatment. Research directions in enzyme technology and their importance for future development in environmental biotechnology are elaborated. Beside biological and biochemical approaches, i.e. enzyme prospection and the design of enzymes, the review also covers efforts in adjacent research fields such as insolubilization of enzymes, reactor design and the use of additives. The effectiveness of enzymatic processes, especially when combined with established technologies, is evident. However, only a limited number of enzymatic field applications exist. Factors like cost and stability of biocatalysts need to be addressed and the collaboration and exchange between academia and industry should be further strengthened to achieve the goal of sustainability.     

Intimate coupling of photocatalysis and biodegradation in a photocatalytic circulating-bed biofilm reactor

Coupling advanced oxidative pretreatment with subsequent biodegradation demonstrates potential for treating wastewaters containing biorecalcitrant and inhibitory organic constituents. However, advanced oxidation is indiscriminate, producing a range of products that can be too oxidized, unavailable for biodegradation, or toxic themselves. This problem could be overcome if advanced oxidation and biodegradation occurred together, an orientation called intimate coupling; then, biodegradable organics are removed as they are formed, focusing the chemical oxidant on the non-biodegradable fraction. Intimate coupling has seemed impossible because the conditions of advanced oxidation, for example, hydroxyl radicals and sometimes UV-light, are severely toxic to microorganisms. Here, we demonstrate that a novel photocatalytic circulating-bed biofilm reactor (PCBBR), which utilizes macro-porous carriers to protect biofilm from toxic reactants and UV light, achieves intimate coupling. We demonstrate the viability of the PCBBR system first with UV only and acetate, where the carriers grew biofilm and sustained acetate biodegradation despite continuous UV irradiation. Images obtained by scanning electron microscopy and confocal laser scanning microscopy show bacteria living behind the exposed surface of the cubes. Second, we used slurry-form Degussa P25 TiO2 to initiate photocatalysis of inhibitory 2,4,5-trichlorophenol (TCP) and acetate. With no bacterial carriers, photocatalysis and physical processes removed TCP and COD to 32% and 26% of their influent levels, but addition of biofilm carriers decreased residuals to 2% and 4%, respectively. Biodegradation alone could not remove TCP. Photomicrographs clearly show that biomass originally on the exterior of the carriers was oxidized (charred), but biofilm a short distance within the carriers was protected. Finally, we coated TiO2 directly onto the carrier surface, producing a hybrid photocatalytic-biological carrier. These carriers likewise demonstrated the concept of photocatalytic degradation of TCP coupled with biodegradation of acetate, but continued TCP degradation required augmentation with slurry-form TiO2.     

Environmental biotechnology: the ongoing quest

Environmental biotechnology, until now, has primarily focused on the development of technologies to treat aqueous, solid and gaseous wastes. At present, the basic knowledge on how biotechnology can handle these wastes has been acquired and the focus is now on the implementation of these processes as 'best available technology not entailing excessive costs' (BATNEEC) in the framework of strict and transparent environmental legislation. New environmental challenges continue to evolve, as it becomes clear that waste streams should be tackled in an overall holistic way. New technologies to reach this goal are currently under development. Novel aspects with respect to the domain of water treatment are, for example, the biomembrane reactor technology and the newly discovered processes to remove nitrogen by means of anaerobic ammonium oxidation. Also, most challenging is the continuing strive for re-use of treated wastewater. Indeed, water shortage is emerging in an increasing number of countries all over the world and necessitates the short cycling of water. Finally, biotechnology has a key role to play in the novel approaches to design wastewater treatment based on decentralised sanitation and reuse (DESAR). Solid waste is a major challenge worldwide. The implementation of anaerobic digestion to treat biowastes has become a grown-up technology. New approaches in which biotechnological processes are linked to physical processes, such as plasma technology, certainly deserve special attention for the coming decades. Soil and sediment clean up by means of biostimulation/remediation/augmentation is now well established. Certainly, a number of prospects need to be further explored, such as the use of special energy sources to stimulate in situ the microbial community and the seeding of knowledge to the in situ community by means of horizontal gene transfer mechanisms. A number of waste gases can be handled by biofilter systems. Biological treatment of wastegases is also evolving, inasmuch as that besides conventional chemical pollutants, now also highly problematic chemicals (even dioxins) can be dealt with through proper biotechnological approaches. A remarkable new potential is the use of well designed probiotics to upgrade aquaculture and together with conventional biological water treatment processes, to guarantee the overall water quality of this domain of food production.     

R&D priorities in the field of sustainable remediation and purification of agro-industrial and municipal wastewater

This article was presented as a position paper during the Environmental Biotechnology and Microbiology Conference in Bologna, Italy in April 2012. It indicates major and emerging environmental biotechnology research and development (R&D) priorities for EU members in the field of sustainable remediation and purification of agro-industrial and municipal wastewater. The identified priorities are: anaerobic/aerobic microbial treatment, combination of photochemical and biological treatment, phytoremediation and algae-based remediation, as well as innovative technologies currently investigated, such as enzyme-based treatment, bioelectrochemical treatment and recovery of nutrients and reuse of cleaned water. State of the art, research needs and prospective development in these domains are crucially discussed. As a result, goals of the future development of bioremediation and purification processes are defined and the way to achieve them is proposed.     

Use of molecular techniques in bioremediation

In a practical sense, biotechnology is concerned with the production of commercial products generated by biological processes. More formally, biotechnology may be defined as "the application of scientific and engineering principles to the processing of material by biological agents to provide goods and services" (Cantor, 2000). From a historical perspective, biotechnology dates back to the time when yeast was first used for beer or wine fermentation, and bacteria were used to make yogurt. In 1972, the birth of recombinant DNA technology moved biotechnology to new heights and led to the establishment of a new industry. Progress in biotechnology has been truly remarkable. Within four years of the discovery of recombinant DNA technology, genetically modified organisms (GMOs) were making human insulin, interferon, and human growth hormone. Now, recombinant DNA technology and its products--GMOs are widely used in environmental biotechnology (Glick and Pasternak, 1988; Cowan, 2000). Bioremediation is one of the most rapidly growing areas of environmental biotechnology. Use of bioremediation for environmental clean up is popular due to low costs and its public acceptability. Indeed, bioremediation stands to benefit greatly and advance even more rapidly with the adoption of molecular techniques developed originally for other areas of biotechnology. The 1990s was the decade of molecular microbial ecology (time of using molecular techniques in environmental biotechnology). Adoption of these molecular techniques made scientists realize that microbial populations in the natural environments are much more diverse than previously thought using traditional culture methods. Using molecular ecological methods, such as direct DNA isolation from environmental samples, denaturing gradient gel electrophoresis (DGGE), PCR methods, nucleic acid hybridization etc., we can now study microbial consortia relevant to pollutant degradation in the environment. These techniques promise to provide a better understanding and better control of environmental biotechnology processes, thus enabling more cost effective and efficient bioremediation of our toxic waste and contaminated environments.     

Biological treatment of high strength wastewater by fed-batch operation

Biological treatment systems for high strength wastewaters are usually operated in continuous mode such as activated sludge systems. When operated at steady-state, continuous systems result in constant effluent standards. However, in the presence of shock loadings and/or toxic compounds in feed wastewater, system performance drops quite significantly as a result of partial loss of microbial activity. In fed-batch operation, wastewater is fed to the aeration tank with a flow rate determined by effluent standards. In this type of operation, wastewater can be fed to biological oxidation unit intermittently or continuously with a low flow rate without any effluent removal. Feed flow rate is adjusted by measuring COD concentration in the effluent. As a result of intermittent addition of wastewater high COD concentrations and toxic compounds are diluted in large volume of aeration tank and inhibition effects of those compounds are reduced. As a result, biological oxidation of these compounds take place at a much higher rate. In order to show the aforementioned advantage of fed-batch operation, a high strength synthetic wastewater consisting of diluted molasses, urea, KH₂PO₄ and MgSO₄ was treated in an biological aeration tank by fed-batch operation. Organisms used were an active and dominant culture of Zooglea ramigera commonly encountered in activated sludge operations. COD removal kinetics was found to be first order and the rate constant was determined.     

Transformation of saturated nitrogen-containing heterocyclic compounds by microorganisms

The saturated nitrogen-containing heterocyclic compounds include many drugs and compounds that may be used as synthons for the synthesis of other pharmacologically active substances. The need for new derivatives of saturated nitrogen-containing heterocycles for organic synthesis, biotechnology and the pharmaceutical industry, including optically active derivatives, has increased interest in microbial synthesis. This review provides an overview of microbial technologies that can be valuable to produce new derivatives of saturated nitrogen-containing heterocycles, including hydroxylated derivatives. The chemo-, regio- and enantioselectivity of microbial processes can be indispensable for the synthesis of new compounds. Microbial processes carried out with fungi, including Beauveria bassiana, Cunninghamella verticillata, Penicillium simplicissimum, Aspergillus niger and Saccharomyces cerevisiae, and bacteria, including Pseudomonas sp., Sphingomonas sp. and Rhodococcus erythropolis, biotransform many substrates efficiently. Among the biological activities of saturated nitrogen-containing heterocyclic compounds are antimicrobial, antitumor, antihypertensive and anti-HIV activities; some derivatives are effective for the treatment and prevention of malaria and trypanosomiasis, and others are potent glycosidase inhibitors.     

Engineering biological systems using automated biofoundries

Engineered biological systems such as genetic circuits and microbial cell factories have promised to solve many challenges in the modern society. However, the artisanal processes of research and development are slow, expensive, and inconsistent, representing a major obstacle in biotechnology and bioengineering. In recent years, biological foundries or biofoundries have been developed to automate design-build-test engineering cycles in an effort to accelerate these processes. This review summarizes the enabling technologies for such biofoundries as well as their early successes and remaining challenges.     

Advanced enzymatic elimination of phenolic contaminants in wastewater: a nano approach at field scale

The removal of recalcitrant chemicals in wastewater treatment systems is an increasingly relevant issue in industrialized countries. The elimination of persistent xenobiotics such as endocrine-disrupting chemicals (EDCs) emitted by municipal and industrial sewage treatment plants remains an unsolved challenge. The existing efficacious physico-chemical methods, such as advanced oxidation processes, are resource-intensive technologies. In this work, we investigated the possibility to remove phenolic EDCs [i.e., bisphenol A (BPA)] by means of a less energy and chemical consuming technology. To that end, cheap and resistant oxidative enzymes, i.e., laccases, were immobilized onto silica nanoparticles. The resulting nanobiocatalyst produced at kilogram scale was demonstrated to possess a broad substrate spectrum regarding the degradation of recalcitrant pollutants. This nanobiocatalyst was applied in a membrane reactor at technical scale for tertiary wastewater treatment. The system efficiently removed BPA and the results of long-term field tests illustrated the potential of fumed silica nanoparticles/laccase composites for advanced biological wastewater treatment.     

Biosorption Processes for Natural and Wastewater Treatment – Part 1: Literature Review

An analysis is made of the literature on the mechanism of biosorption‐bioregeneration of organic substances mainly on activated carbon (AC). There have advanced two hypotheses on the biosorption mechanism: the Rodman exoenzymatic hypothesis and the bioregeneration approach of Andrews and Chi Tien. In addition, it was shown that the principal mechanism responsible for the removal of both biodegradable and bioresistant compounds is biological oxidation, but only in combination with adsorption on activated carbon. The authors examine the role of the filter medium in biosorption, factors affecting efficiency of biosorption and bioregeneration of AC and technological aspects of the application of biosorptive processes.     

嗜热古菌异化型硫氧化途径的研究进展

微生物参与的还原性无机硫化合物的氧化过程是硫地球化学循环的重要组成部分,也可应用于生物冶金工业及酸性矿水治理等方面。嗜热古菌是高温环境中存在的一群特殊的微生物,其所参与的异化型硫氧化途径复杂多样,涉及众多氧化还原酶以及硫转运蛋白。本文将结合我们的研究工作,就参与异化型硫氧化代谢过程的嗜热古菌的种类,以及它们所参与的硫氧化过程进行系统的介绍。     

Next‐generation bioproduction systems: Cell‐free conversion concepts for industrial biotechnology

Within the last decade, biotechnology gained pace in substituting petro‐based products for the chemical industries. This is visible with the appearance of bio‐based products in the market, from biosurfactants to bio‐based polymers like polylactic acid to bio‐ethylene. These technologies are mainly based on established fermentation technologies fostered by the use of renewable resources, culminating in the establishment of biorefineries that may be connected directly to the existing chemical infrastructure. Besides these large‐scale technologies, the combination of molecular technologies, microfluidic devices, and enzymatic and cell‐free conversions are currently developed to create new bioproduction systems enabling the production of compounds that may not be produced within a cell. This article summarizes some of the current ideas that are currently in development paving the way for a next generation of biotechnology.     

Low-temperature extremophiles and their applications

Psychrophilic (cold-adapted) organisms and their products have potential applications in a broad range of industrial, agricultural and medical processes. In order for growth to occur in low-temperature environments, all cellular components must adapt to the cold. This fact, in combination with the diversity of Archaea, Bacteria and Eucarya isolated from cold environments, highlights the breadth and type of biological products and processes that might be exploited for biotechnology. Relative to this undisputed potential, psychrophiles and their products are under-utilised in biotechnology; however, recent advances, particularly with cold-active enzymes, herald rapid growth for this burgeoning field.     

污水处理工艺的生态安全性研究进展

污水经处理后,排放和回用时常规指标通常都能达到设计标准,但出水水质并未达到无害化.从可持续发展的角度来讲,为保障生态环境及人群的安全,需要将污水的综合毒性纳入排放标准.为此,在工艺的选择及优化时应将毒性削减效果纳入其中,提高污水处理工艺的生态安全性.本文着重综述了以特定污水处理为目的、以污水回用为目的及以受纳水体安全为目的各类污水处理工艺的生态安全性研究,指出传统生物处理与高级氧化技术相结合,在去除污染物质的基础上可以强化对毒性的削减;对于以污水回用为目的处理工艺,对各种工艺进行集成可实现常规污染物去除和毒性削减的优势互补;以受纳水体生态安全为目的的污水处理工艺,应重点基于工艺运行参数和工艺单元选择进行毒性削减优化.最后对研究中存在的问题以及未来的学科发展方向提出了建议.     

Microbiological and biotechnological aspects of metabolism of carbamates and organophosphates.

Several carbamate and organophosphate compounds are used to control a wide variety of insect pests, weeds, and disease-transmitting vectors. These chemicals were introduced to replace the recalcitrant and hazardous chlorinated pesticides. Although newly introduced pesticides were considered to be biodegradable, some of them are highly toxic and their residues are found in certain environments. In addition, degradation of some of the carbamates generates metabolites that are also toxic. In general, hydrolysis of the carbamate and organophosphates yields less toxic metabolites compared with the metabolites produced from oxidation. Although microorganisms capable of degrading many of these pesticides have been isolated, knowledge about the biochemical pathways and respective genes involved in the degradation is sparse. Recently, a great deal of interest in the mechanisms of biodegradation of carbamate and organophosphate compounds has been shown because (1) an efficient mineralization of the pesticides used for insect control could eliminate the problems of environmental pollution, (2) a balance between degradation and efficacy of pesticides could result in safer application and effective insect control, and (3) knowledge about the mechanisms of biodegradation could help to deal with situations leading to the generation of toxic metabolites and bioremediation of polluted environments. In addition, advances in genetic engineering and biotechnology offer great potential to exploit the degradative properties of microorganisms in order to develop bioremediation strategies and novel applications such as development of economic plants tolerant to herbicides. In this review, recent advances in the biochemical and genetic aspects of microbial degradation of carbamate and organophosphates are discussed and areas in need of further investigation identified.