Editorial In Focus: Wastewater treatment
The world is running out of water. In many parts of the world, surface waters are too polluted for human use. It is estimated that 90% of wastewater in the Third World is disposed of untreated. About a sixth of the Earth's population have no access to drinking water, while according to the World Health Organization (WHO), five million people die each year from poor drinking water, poor sanitation and a dirty home environment often owing to water shortage. From this perspective, wastewater is regarded nowadays as a resource rather than a waste and research is being conducted to devise new technologies or improve existing ones that would optimize treatment and yield a product suitable for reclamation and reuse. Fundamental and applied research on effluent treatment covers virtually everything, i.e. various biological, physical and chemical processes to remove biological, physical and chemical contaminants from sewage and industrial effluents. This broad array of activities is highlighted in this ''In Focus'' issue devoted to wastewater treatment.
Sewage treatment is the topic of the first two articles. The work of Zhao et al. 1 investigates the effect of varying C/N and C/P ratios as well as the volumetric exchange ratio on tertiary treatment in the so-called UniFed sequencing batch reactor (SBR) process. The process features suitable conditions for denitrification and anaerobic phosphate release, thus enhancing biological phosphorous removal; the latter is maximized at increased C/N, C/P and exchange ratios. Zhou et al. 2 apply the activated sludge model (ASM) to evaluate the effect of pipeline retention time and stormwater runoffs on COD fractionation and degradation kinetics in combined sewer systems. Long pipeline transportation strongly influences COD fractionation but not the kinetics with the exception of hydrolysis rates. Moreover, model calibration is needed to account for wet weather conditions.
Environmental biotechnology can offer simple and effective solutions for industrial effluent treatment. This is highlighted in the work of Xavier et al. where the white rot fungus Trametes versicolor is employed for the treatment of kraft pulp mill effluents in Sequencing Batch Reactor (SBR) processes. The authors adopt a factorial design methodology to first elucidate and then optimise the statistically significant parameters (i.e. effluent concentration, culture medium and inoculum age). Water pollution associated with textile manufacturing has long been alarming in several parts of the world as effluents containing spent dyes are often coloured and highly toxic. Tavares et al. carry out a comprehensive study on the laccase-catalysed decolourisation of six reactive textile dyes to determine key operating conditions; these include the type and concentration of laccase mediator (five electron carriers are tested), temperature and solution pH.
A major source of heavy metal pollution in the environment is from industrial and mining wastewater. Chromium passivation baths used in the electroplating industry become progressively contaminated with iron and zinc impurities and, unless they can somehow be regenerated, they are considered as hazardous wastes. This is the theme of the work of FernΓ‘ndez-Olmo et al. 5 who test a new chelating resin for the selective removal of iron from spent baths containing zinc and trivalent chromium. The resin shows great affinity to iron and excellent chemical stability and its performance depends on the operating temperature and flowrate. In a similar fashion, Ma et al. 6 employ an iminodiacetate resin for the removal of nickel from aqueous solutions and focus on the impact of initial nickel concentration, resin loading and particle size on separation. The equilibrium is best described by the Redlich-Peterson isotherm (basically a combination of the Langmuir and Freundlich equations), while sorption kinetics follows the empirical Elovich model. Nickel separation can also be accomplished through its biosorption onto the fungus Rhizopus arrhizus as demonstrated by Tahir and Zahid 7 . The uptake of nickel from an electroplating industry effluent is a function of several parameters such as nickel concentration, incubation temperature and pH, contact time and the relative concentration of dead and alive biomass. Although biosorption is a process more frequently applied to heavy metals removal, organic contaminants may also be treated this way. Li et al. 8 evaluate the biosorption potential of softstem bulrush for the removal of methylene blue from water. The process follows a pseudo-second order kinetic expression, thus implying that chemisorption is the rate-limiting mechanism, while equilibrium is described by the Langmuir isotherm.
In this issue, we have collated eight papers (including a technical note) ''In Focus'' to demonstrate the variety of fundamental research activities and applications in the field of wastewater treatment. This is a pivotal area for the journal as it steps at the interfaces between chemical technology and biotechnology and has a clear impact on health and the environment. The Editors of JCTB welcome high quality submissions in the area of water and wastewater treatment.