Ji Dai

(Photo)chlorination-induced physicochemical transformation of aqueous fullerene nC60.

This study confirmed the physicochemical transformation of aqueous fullerene aggregates (nC(60)) produced via solvent exchange from toluene by chlorine in the dark and under fluorescent light (representing visible light) by comparing the changes in light absorbance at 700 nm and size distribution of nC(60) and characterizing the photochlorination products of nC(60) by XPS, FTIR and TOF-SIMS techniques. The (photo)chlorination of nC(60) was enhanced by increasing the chlorine dosage and the salinity concentration, and the presence of fluorescent light. During (photo)chlorination, nC(60) underwent surface chlorination, hydroxylation and oxidation, and was transformed into products containing carbon-chlorine, epoxy and hydroxyl functional groups. Extensive (photo)chlorination produced products that might not possess the isolated benzenoid ring structure on their cages, although they retained the 60-carbon cage structure. These findings imply the necessity of assessing the fate and toxicity of nC(60) after (photo)chlorination in both engineered and natural environments and demonstrate a simple way to produce new nC(60) derivatives that contain chlorine and oxygen.

Pilot trial study of a compact macro-filtration membrane bioreactor process for saline wastewater treatment

Conventional membrane bioreactor (MBR) systems have increasingly been studied in recent decades. However, their applications have been limited due to their drawbacks such as low flux, membrane fouling, and high operating cost. In this study, a compact macro-filtration MBR (MfMBR) process was developed by using a large pore size membrane to mitigate the membrane fouling problem. A pilot trial of MfMBR process was set up and operated to treat 10 m(3)/day of saline wastewater within 4 h. The system was operated under an average permeate flux of 13.1 m(3)/(m(2)·day) for 74 days. The average total suspended solids, total chemical oxygen demand, biological oxygen demand, total Kjeldahl nitrogen, and total nitrogen removal efficiencies achieved were 94.3, 83.1, 98.0, 93.1, and 63.3%, respectively, during steady-state operation. The confocal laser scanning microscopy image indicated that the backwash could effectively remove the bio-cake and dead bacteria. Thus, the results showed that the MfMBR process, which is essentially a primary wastewater treatment process, had the potential to yield the same high quality effluent standards as the secondary treatment process; thereby suggesting that it could be used as an option when the economic budget and/or land space is limited.

Microbial ureolysis in the seawater-catalysed urine phosphorus recovery system: Kinetic study and reactor verification

Our previous study has confirmed the feasibility of using seawater as an economical precipitant for urine phosphorus (P) precipitation. However, we still understand very little about the ureolysis in the Seawater-based Urine Phosphorus Recovery (SUPR) system despite its being a crucial step for urine P recovery. In this study, batch experiments were conducted to investigate the kinetics of microbial ureolysis in the seawater-urine system. Indigenous bacteria from urine and seawater exhibited relatively low ureolytic activity, but they adapted quickly to the urine-seawater mixture during batch cultivation. During cultivation, both the abundance and specific ureolysis rate of the indigenous bacteria were greatly enhanced as confirmed by a biomass-dependent Michaelis-Menten model. The period for fully ureolysis was decreased from 180 h to 2.5 h after four cycles of cultivation. Based on the successful cultivation, a lab-scale SUPR reactor was set up to verify the fast ureolysis and efficient P recovery in the SUPR system. Nearly complete urine P removal was achieved in the reactor in 6 h without adding any chemicals. Terminal Restriction Fragment Length Polymorphism (TRFLP) analysis revealed that the predominant groups of bacteria in the SUPR reactor likely originated from seawater rather than urine. Moreover, batch tests confirmed the high ureolysis rates and high phosphorus removal efficiency induced by cultivated bacteria in the SUPR reactor under seawater-to-urine mixing ratios ranging from 1:1 to 9:1. This study has proved that the enrichment of indigenous bacteria in the SUPR system can lead to sufficient ureolytic activity for phosphate precipitation, thus providing an efficient and economical method for urine P recovery.

Comparison of the cytotoxic responses of Escherichia coli (E. coli) AMC 198 to different fullerene suspensions (nC60).

Fullerenes are set to be produced on an industrial scale in anticipation of their wide applications. This calls for research on their environmental and health impacts. This study investigates and compares the cell toxicity of different aqueous fullerene aggregates. Popular C(60) dispersal methods were used to prepare four types of nC(60) aggregates. These aggregates were tested against the indicator species Escherichia coli (E. coli) AMC 198. With aggregates of around 150 nm in diameter, the THF/nC(60) suspension was very toxic and gave rise to a half maximal effective concentration (EC(50)) of 0.54 mg L(-1) in E. coli. By contrast, the Tol/nC(60) suspension exhibited a cytoprotective role while the Aqu-N(2)/nC(60) and Aqu-O(2)/nC(60) suspensions enhanced the metabolism of E. coli. Although some toxicants, such as THF and THF-peroxide, were introduced into the THF/nC(60) suspension during the dispersion, the toxicity of nC(60) itself cannot be neglected.

Changes in the physical properties of the dynamic layer and its correlation with permeate quality in a self-forming dynamic membrane bioreactor

The self-forming dynamic membrane bioreactor (SFDMBR) is a biological wastewater treatment technology based on the conventional membrane bioreactor (MBR) with membrane material modification to a large pore size (30-100 μm). This modification requires a dynamic layer formed by activated sludge to provide effective filtration function for high-quality permeate production. The properties of the dynamic layer are therefore important for permeate quality in SFDMBRs. The interaction between the structure of the dynamic layer and the performance of SFDMBRs is little known but understandably complex. To elucidate the interaction, a lab-scale SFDMBR system coupled with a nylon woven mesh as the supporting material was operated. After development of a mature dynamic layer, excellent solid-liquid separation was achieved, as evidenced by a low permeate turbidity of less than 2 NTU. The permeate turbidity stayed below this level for nearly 80 days. In the fouling phase, the dynamic layer was compressed with an increase in the trans-membrane pressure and the quality of the permeate kept deteriorating until the turbidity exceeded 10 NTU. The investigation revealed that the majority of permeate particles were dissociated from the dynamic layer on the back surface of the supporting material, which is caused by the compression, breakdown, and dissociation of the dynamic layer. This phenomenon was observed directly in experiment instead of model prediction or conjecture for the first time.

Combined seawater toilet flushing and urine separation for economic phosphorus recovery and nitrogen removal: a laboratory-scale trial

Freshwater toilet flushing consumes 20-35% of typical household water demand. Seawater toilet flushing, as practised by Hong Kong since 1958, provides an alternative water source. To maximise the benefits of this unique dual water supply, urine separation could be combined to allow low-cost struvite production and subsequent urine nitrification - in-sewer denitrification. This paper reports on a laboratory-scale study of seawater urine phosphate recovery (SUPR) and seawater-urine nitrification. A laboratory-scale SUPR reactor was run under three phases with hydraulic retention time between 1.5 and 6 h, achieving 91-96% phosphorus recovery. A urine nitrification sequencing batch reactor (UNSBR) was also run for a period of over 650 days, averaging 90% ammonia removal and loading of up to 750 mg-N/L.d. Careful control of the SUPR phosphate removal was found necessary for operation of the downstream UNSBR, and system integration considerations are discussed.

The Impact of Chlorine Disinfection on Biochemical Oxygen Demand Levels in Chemically Enhanced Primary Treatment Effluent

The response trends of biochemical oxygen demand (BOD) and organic strength after the chlorination/dechlorination process were explored through a 2-year, 5-month chemically enhanced primary treatment (CEPT) effluent onsite monitoring program and a 2-month laboratory-scale study. The monitoring results showed that better instantaneous mixing at the chlorine injection point reduced the effect of chlorination/dechlorination on the 5-day BOD levels. The laboratory study results demonstrated that chlorination did not change the particle size distribution, dissolved organic carbon, or chemical oxygen demand of the organic content of the effluent. Nevertheless, chlorination/dechlorination strongly affected the BOD measurement when nitrification was inhibited by changing bioactivity/biodegradation rates.

The characteristics of household food waste in Hong Kong and their implications for sewage quality and energy recovery

Food waste (FW) is a worldwide environmental issue due to its huge production amount. FW separation from municipal solid waste followed by different treatment strategies has been widely accepted. Food waste disposer (FWD) is a promising approach to separate and collect household food waste (HFW), which has been widely applied in many countries. However, the feasibility of FWD application in many countries is still being debated due to the major concerns over the impact of FWD on the wastewater treatment plants. In order to investigate the feasibility of FWD application, FW characterization is a key work to be conducted in advance. Since the FW characteristics largely vary by region, reliable and representative FW characteristics in different countries should be investigated. To provide such information for further studies on FW management for Hong Kong, HFW was collected from Hong Kong typical households over one year and analyzed systemically in this study. The FW composition varied little from place to place or season to season, and the values observed were comparable with results reported from other countries and regions. Based on the reliable HFW characteristics obtained from one-year survey coupled with statistical analysis, simulated HFW for Hong Kong consisting of 50% fruits, 20% vegetables, 20% starchy food and 10% meat was proposed for future studies. On the other hand, the FWD treatment caused more than 50% of the biodegradable organic content in HFW to dissolve. With a ratio of 1 g food waste to 1 L sewage, total solids in the wastewater stream were predicted to increase by 73%, total chemical oxygen demand by 61%, soluble chemical oxygen demand by 110%, nitrogen by 6% and phosphorus by 16%. Theoretically, 22 million m3/year of additional methane could be generated if 50% of Hong Kong residential buildings equipped with FWD. That would certainly increase pollutant loading on the wastewater treatment plants, but also energy recovery potential.