Goen Ho

In recent years, forward osmosis (FO) has been attracting an intensive research interest due to its potential for low-energy water desalination and wastewater treatment. Membrane fouling, especially that caused by polysaccharides, has been regarded as one of the significant challenges retarding the development of FO process in various applications. In order to efficiently alleviate polysaccharide fouling in FO separation, it is necessary to strengthen the fundamental understanding on its mechanisms. This study systematically investigated the fouling behaviors of different polysaccharides, namely alginate, xanthan and pullulan, in FO. The three selected model foulants behaved differently; specifically the polysaccharide solution of high viscosity in the presence of calcium ions are likely to lead to severe membrane fouling, due to adsorption and accumulation of the polysaccharide on the membrane surface.

Reusing greywater from laundry and bathtub is an option for residents wanting to keep their gardens and lawns green, especially when water restrictions are in place during summer period. The present study was carried out to evaluate the effects of laundry and bathtub greywater irrigation in sands on the growth of couch grass (Cynodon dactylon L.) sod in a tank experimental study. Untreated laundry and bathtub greywater collected from a residential home were monitored for sodium (Na), chlorine (Cl) and boron (B), as these elements are dominant in household detergent and cleaning products. The turf grasses were planted in the modified aquarium tank with triplicate for each irrigation type. Irrigation sources included (i) 100% potable water as a control (TW) (ii) untreated full cycle laundry water (LGW) (iii) untreated bathtub water (BGW) over 24 weeks, starting from October 2009 to March 2010. The reduction on soil hydraulic conductivity was tested using double rings infiltrometer. A mass balance was carried out to determine the amount of Na, Cl and B flowing into and out of the tank. The results showed that the high salt (Na, Cl) and B content was significant in laundry greywater compared to bathtub. Irrigation with laundry and bathtub greywater without fertilizer addition was insufficient to sustain the turf growth. Long-term use of laundry and bathtub greywater can lead to salt and metal accumulation in the soil and subsequent uptake by the turf grass. Turf grass established well at the first 8 week irrigated with LGW and BGW, but did not survive after 16 weeks of study. There was a greater reduction of growth in species that accumulated more salt and B. Consequently, the turf grass requires an addition of nutrients in its fertilization program in order to sustain the turf grass growth.

Vermifiltration systems rely on the biodegradation of organic matter in household wastewater to produce a humus filter. The humus filter in an appropriate design is capable of treating wastewater to a high secondary standard suitable for non-contact reuse purposes e.g. irrigation. The variable nature of household wastewater production and constitution may cause toxicity from particular wastewater constituents to the species that biodegrade the organic matter in vermifiltration systems. Due to this, this study was undertaken to assess the toxicity of one particular constituent, hypochlorite, to key species within the vermifiltration process. Hypochlorite and its by-products are present in many household products, especially disinfectants and household cleaners.

During the study, the key vermifiltration species, the worm Eisenia fetida, was subjected to a series of hypochlorite toxicity tests in solid phase mesocosms. The tests showed that the adult worms were relatively tolerant to hypochlorite toxicity, but the reproduction by the worms was impaired at a very low hypochlorite concentration. The overall risk assessment showed that hypochlorite and its main by-products total organic halogens and sodium chloride are unlikely to cause toxicity to E fetida from accumulation in a vermifiltration system, during normal household use.