Water Research 86 (2015) 83e84
Contents lists available at ScienceDirect
Water Research journal homepage: www.elsevier.com/locate/watres
Editorial
Resource recovery: Efficient approaches to sustainable water and wastewater treatment
Now that sustainability is becoming a major concern, it is important that water problems are solved in a more integrated and innovative way. It is therefore essential that more sustainable processes be developed. What is pursued in sustainable processes is the recovery of all useful resources such as chemicals, nutrients, energy, and water itself. In this respect, wastewater can be viewed as a carrier of resources and energy. After nutrients and organic (COD) energy have been recovered, effluent, as a byproduct, can then be reused. This is quite different to traditional processes, as it pursues effluent as a main product regardless of other resources and energy recovery. In fact, organic energy recovery can contribute considerably to reducing both sludge production and CO2 emissions, and phosphate recovery can alleviate depletion of phosphorus deposits on Earth. Moreover, utilizing or recovering residues from drinking water, harvesting stormwater and even producing biofuel with wastewater and microalgae can all contribute to sustainability in water use. This special issue is related to one of two sessions on the 3rd Water Research conference (held in Shenzhen/China on January 11e14, 2015), which aimed to discuss new concepts and ideas crucial to the development of well-tuned energy- and resourceefficient treatment technologies designed to recover increasingly limited and valuable resources such as nutrients, energy and water. After peer review, 6 of 54 submitted articles were selected for publication. Although the selected articles can not cover the entire range of resource and energy recovery as mentioned above, they present an overview of the state-of-the-art exploration being conducted into resource and energy recovery. 1. New insights into the role of EPS in maximizing P-recovery in EBPR processes P-recovery from wastewater would be more effective with a combination of chemical and biological methods of removal, as chemical precipitation normally has a macro-quantity effect and biological uptake has a superior micro-quantity effect, at an appropriate COD/P ratio. In this way, side-stream of anaerobic supernatant in EBPR processes is an ideal point (where there is usually a high phosphate concentration between 20 and 60 mg P/L) to precipitate/recover phosphate. After phosphate recovery, the phosphate-reduced supernatant can be returned to subsequent biological (anoxic and aerobic) units where a remarkably increased COD/P ratio appears. As a result, both P-recovery and low P-effluent can easily be produced. In other words, a high phosphate http://dx.doi.org/10.1016/j.watres.2015.10.063 0043-1354/© 2015 Published by Elsevier Ltd.
concentration in anaerobic supernatant is most effective. Recent studies have revealed considerable P-accumulation in the EPS of PAOs, which implies a non-negligible role of EPS in Premoval/recovery in EBPR processes. A review (Li et al.) summarizes the characteristics of P-accumulation in EPS and the associated influential factors. Special emphasis is put on the mechanisms of P-transformation and transportation in EPS with the PAOs' metabolism and P-precipitation processes taken into consideration. The knowledge gaps between the design and management of EBPR processes are identified efficiently and reliably. This review expands our knowledge of EBPR processes and, it is hoped, will provide guidance for developing more efficient, stable and sustainable P-removal/recovery processes. 2. Organic energy conversion and carbon capture Organic energy conversion from wastewater usually depends on anaerobic digestion of excess sludge/highly concentrated organic wastewater. A newly developed technology e MFCs e has recently been employed to generate electricity directly from organic matter (COD) in wastewater. AnMBRs are regarded as one potential way of achieving energy neutrality in future WWTPs. Coupling ceramic membranes to AnMBRs is also considered to have great potential, as ceramic membranes are resistant to corrosive chemicals such as cleaning reagents and harsh environmental conditions, such as high temperatures. A study (Yue et al.) revealed that different ceramic membranes with pore sizes of 80, 200 and 300 nm demonstrated an average overall COD removal efficiency of 87% and showed CH4 production of around 0.3 L/g COD being utilized. However, about 2/3 of CH4 generated was dissolved in the liquid phase and lost in permeate. In order to minimize energy wastage, dissolved CH4 must be recovered. Effects of DOMs on membrane fouling were identified to be biopolymers that were produced in microbial activities. One of the main components of biopolymers - proteins - led to different fouling behaviors. It is postulated that the proteins could pass through porous cake layers to create pore blockages in membranes. Hence, concentrations of the DOMs in the soluble fraction of mixed liquor could not be used to predict membrane fouling because different components in the DOMs might have different ways of interacting with membranes. Another study (Gajda et al.) with an MFC unit not only demonstrated the potential for electricity generation potential (309 mW), but also revealed the possibility of capturing carbon dioxide from
84
Editorial / Water Research 86 (2015) 83e84
the environment with the help of recovered water and forming caustic catholyte in the cathode electrode. Caustic catholyte was mineralized to a mixture of carbonate and bicarbonate (trona) salts, thus demonstrating a carbon-capturing mechanism as an active result of MFC performance. Carbon capturing would be valuable for establishing a carbon-negative economy and environmentally sustainable wastewater treatment process. 3. Stormwater harvesting and LID application Stormwater harvesting for non-drinking purposes has been emphasized in some areas suffering from water-shortages in recent years. Rapid urbanization, however, often results in an increase in impervious areas and surface runoff, including pollutants. In addition, one of the greatest issues in pollutant emission is the first flush effect (FFE) in storms. Because of this, low impact development (LID) practices have been developed as a promising strategy to control urban stormwater runoff and pollution in the urban ecosystem. A study (An et al.) evaluated a rooftop garden with stormwater harvesting facilities for temperature reduction in Hong Kong. In terms of the cooling effect, the implementation of a rooftop stormwater harvesting garden was evaluated using the ENVI-met model. The results show that a temperature drop of 1.3 C has been observed due to the rainwater layer in the rain garden. This study provides valuable insights into the applicability of the stormwater harvesting for sustainable water management practice in a highly urbanized city. Another study (Baek et al.) indicated that testing LID characteristics and proposing an adequate guideline for optimizing LID management required many experimental and modeling efforts. The study proposes a novel methodology for optimizing the sizes of different types of LID by conducting intensive stormwater monitoring and numerical modeling in a commercial site in Korea. The methodology optimized LID size in an attempt to moderate FFE on a receiving water body. The optimal sizes of 6 different LIDs ranged from 1.2 mm to 3.0 mm in terms of runoff depths. The new proposed methodology is instructive for establishing LID strategies to mitigate FFE. 4. Enhanced microalgae cultivation and oxygen production Lagoons provide a demonstration of a simple approach to
treating wastewater, having an algal-bacterial symbiotic system which functions naturally. As some microalgae contain a certain amount of oil content, microalgae cultivation is currently being emphasized. Algal biofuel production is thought to help stabilize the concentration of carbon dioxide in the atmosphere and decrease the impact of global warming. In addition, among the most appealing features of algal fuels, algal biodiesel is non-toxic, contains no sulfur, is highly biodegradable, and is relatively harmless to the environment if spilled. Algae are capable of producing in excess of 30 times more oil per acre than corn and soybean crops. However, algal biofuel production has not been commercialized due to high costs associated with production, harvesting and oil extraction. For this reason, the technology is still progressing, especially in combination with wastewater treatment. A study (Tu et al.) attempted to utilize the biological synergism of the physiological functions of both algae and bacteria for microalgae cultivation with municipal wastewater. It proposed and tested a novel approach to enhancing algal growth and oxygen production with a static magnetic field. The performance of oxygen production with the applied magnetic field was evaluated using Scenedesmus obliquus growing in municipal wastewater. The results indicate that magnetic treatment stimulated both algal growth and oxygen production. Application of 1000 GS of magnetic field once at logarithmic growth phase for 0.5 h increased the chlorophyll-a content by 11.5% over the control after 6 days of growth. In addition, magnetization enhanced the oxygen production rate by 24.6% over the control. Xiaodi Hao* Beijing University of Civil Engineering and Architecture, China Hiroaki Furumai University of Tokyo, Japan Guanghao Chen Hong Kong University of Science and Technology, China *
Corresponding author. E-mail address:
[email protected] (X. Hao).
