Current Environmental Engineering (v.2, #1)

Meet Our Associate Editor: by Jimmy C.M. Kao (1-1).

Preface: by Jong Moon Park (2-2).

A post-denitrification membrane bioreactor (MBR) system was developed to simultaneously remove organics and nitrogen from domestic wastewater. From a long-term experimental investigation, more than 96% organics could be degraded biologically and the effluent Chemical Oxygen Demand (COD) was below 10.5 mg/L. With a Hydraulic Retention Time (HRT) of 13.6 h and a total recirculation ratio of 8xQ, the MBR system could obtain a stably high Total Nitrogen (TN) removal efficiency of up to 92.4%, resulted in an effluent TN content of as low as 2.80 mg/L. Effects of operating parameters, including HRT, Sludge Retention Time (SRT), recirculation ratio and influent C/N, onto the system treatment performance were evaluated. It was revealed that HRT and recirculation ratio had significant impacts onto TN removal efficiency, reflected by that a reduced HRT to 9 h and a lower recirculation of 6xQ induced to 78.2% TN removal and an effluent TN of about 14 mg/L. A proper SRT and C/N ranged from 12 to 40 days, and from 8:1 to 13.5:1, respectively, have insignificant impacts onto the organic degradation and ammonia-N removal. Nevertheless, TN removal was highly inhibited by low SRT and C/N ratios. MBR combination with post-denitrification helps to enhance the organic and nitrogen removal compared with conventional activated sludge process, as it ensured a high biomass level in the treatment system.

Calibration of ASM-SMP Model Under Specific Experimental Conditions for Membrane Bioreactor Application by Ameni Lahdhiri, Aicha Gasmi, Geoffroy Lesage, Ahmed Hannachi, Marc Heran (11-18).
Membrane bioreactors (MBR) are nowadays increasingly used in the urban wastewater treatment field, particularly those with submerged configuration. This interest in MBR goes necessarily with the need to develop models that are able to describe accurately their operation. In this paper, two biological pathways are introduced to evaluate the influence of heterotrophic biomass growing on substrate that is coming exclusively from the decay of autotrophic biomass. The aim of this work is indeed to assess the importance of heterotrophic biomass growing on debris of autotrophic biomass when no exogenous carbon sources are available. Consequently, a modified ASM1 model called ASM1-SMP model is developed and then calibrated. The obtained model is used to investigate the influence of operand parameters on soluble organic matter. Simulations highlight the growth potential of one fraction (SUAP) of this unconventional carbon source and the advantage of heterotrophic bacteria to decrease the SOM concentration. Nevertheless, SBAP was found to be poorly biodegradable and then dangerously rises in the reactor in case of total retention by the membrane cut-off.

Membrane fouling of forward osmosis (FO) membrane remains as one of major obstacles of osmotic membrane bioreactors (OMBRs); however, the literature on calcium induced inorganic fouling of FO membrane is still limited. In order to better understand the fouling mechanisms of FO membrane in OMBRs, it is necessary to investigate the impacts of calcium on FO membrane fouling. Based on the possible interference of high salinity, novel OMBRs combined with micro-filtration (MF) membrane (MF-OMBRs) for salinity control were applied in this study to evaluate the impacts of high calcium concentration on FO membrane fouling. The results indicated that the calcium concentration of 12.5 mM had no impacts on the removals of total organic carbon (TOC) and ammonium nitrogen (NH3- N) in MF-OMBRs, but resulting in a serious flux decline of FO membrane from approximately 9.2 LMH to 5 LMH. The high calcium concentration level could reduce the thickness of biofouling layer and the adsorption of EPS to the FO membrane surface due to the EPS decrease in the activated sludge through the bridging effect of Ca2+, thus mitigating the biofouling of FO membrane in MF-OMBRs. However, due to the severer calcium induced inorganic fouling at Ca2+ concentration of 12.5 mM, the high calcium concentration level would absolutely deteriorate the FO membrane fouling including reversible and irreversible fouling in MF-OMBRs.

In many countries, nitrate concentrations in surface and ground water have exceeded the concentrations set by drinking water regulations. Hence, several strategies for management, control and the treatment of drinking water resources have been developed in recent years. Although several physicochemical treatment alternatives are in use, they have high construction and operational costs. Also, the secondary brine or concentrated waste is generated after physicochemical treatment processes. Hence, biological denitrification can be considered as an alternative for drinking water treatment. However, the contamination risk of the drinking water by microorganisms and the organic/inorganic nutrients during the denitrification process is the major concern and the biological treatment of drinking water may attract the negative public reaction. In order to eliminate or minimize the risks, membrane-based biological denitrification technologies, including both autotrophic and heterotrophic processes have been developed for drinking water treatment. In this review, membrane-based bioprocesses have been presented together with their advantages/disadvantages and the selection criteria. In this context, heterotrophic membrane bioreactor (MBR), extractive MBR, hydrogen-based membrane biofilm reactor (MBfR), and the autotrophic sulfur-based MBR processes have been comparatively discussed.

Electrochemical Membrane Bioreactors for Sustainable Wastewater Treatment: Principles and Challenges by Jinxing Ma, Zhiwei Wang, Bin Mao, Junyao Zhan, Zhichao Wu (38-49).
Membrane bioreactor (MBR) is a reliable and promising technology for wastewater treatment and reclamation. Recently, the electrochemical process has been integrated into MBRs, which refers to as an electrochemical membrane bioreactor (EMBR). In this paper, fundamental information of EMBRs, including reactor design and construction materials, is critically reviewed. Comprehensive assessment regarding EMBR performances and their economic and environmental significances is presented based on the recent publications. The existing challenges and future research prospects of EMBRs towards practical applications are also discussed.

Effects of Van Der Waals Surface Energy on Membrane Fouling in a Submerged Membrane Bioreactor (MBR) by Tongli Lai, Liguo Shen, Meijia Zhang, Yiming He, Hongjun Lin (50-55).
Effects of van der Waals surface energy (? LW ) on interfacial interactions in a submerged membrane bioreactor (MBR) were investigated by a series methods based on the extended Derjaguin- Landau-Verwey-Overbeek (XDLVO) theory in this study. Interfacial interactions in three different interaction scenarios, including two infinite planar system, particle-smooth surface membrane system, and particle-rough surface membrane system, were systematically assessed. The calculation results implicated that ? LW played a significant role in the interfacial interactions in all three interaction scenarios. There exists an energy barrier in the process of foulant particles' adhesion on membrane surface. It was found that the energy barrier would disappear when a critical? LW was reached. Low ? LW would increase the energy barrier, and then benefit membrane fouling mitigation. Rough surface would significantly reduce interfacial interaction strength.

Current studies explore the viability, applicability and comparison of Pseudomonas aeruginosa and Pseudomonas stutzeri based biological denitrification of waters containing high concentration of nitrate and nitrite waste originating from various agricultural and industrial sources. This process converts the readily soluble nitrates to harmless nitrogen gas through a formation of series of intermediates. Experimental work involved use of varying concentration of nitrates and nitrites with different packing conditions, substrates and were analyzed by UV-Vis spectrophotometer. The parameters such as C/N ratio, temperature and pH were optimized for decreasing concentration of nitrates and nitrites. Best packing materials for nitrate reduction proved to be the agro waste based materials which have potential to be used for nitrate reduction of various waste water samples obtained around the city. Average nitrate reduction rates obtained for agro based waste packing condition exhibited about 96.55% and 95% for Pseudomonas aeruginosa and Pseudomonas stutzeri respectively. When applied for denitrification of waste water sample using the obtained reaction parameters, average nitrate reduction obtained was 53.84% and 33.72% for Pseudomonas aeruginosa and Pseudomonas stutzeri respectively. Based on the obtained observations and experimental results, general bioreactor for denitrification process has been designed.

Design and Pilot Scale Application of a New Geocomposite for Capping of Contaminated Soil by Vassilis Zotiadis, Akindynos. Kelepertsis, A. Kollios (64-69).
This paper presents a pilot scale application of a new type Geosynthetic Clay Composite for environmental applications in the treatment of toxic metals contaminated land. The designed new geocomposite was consisted of a thin layer of permeable, attapulgite clay sandwiched between two geotextiles. To demonstrate its effectiveness a pilot scale application was implemented at a public primary school in Lavrion Greece, an area affected by extensive heavy metal soil pollution due to past metallurgical activities. The attapulgite clay in the geocomposite is an effective binder for the sorption/ adsorption of toxic metals, preventing upwards migration of metals from the contaminated subsoil to the top soil during evaporation. Also the used geotextiles ensured encapsulation but allowed downwards water infiltration. An extensive investigation of the physical and mechanical properties of this geocomposite was performed by testing both short and long-term behavior in this specific application. Environmental monitoring results over a three semester period indicated the long-term effectiveness of the applied remediation technique for toxic metal retention.