Novel membrane bioreactor (MBR) coupled with a nonwoven fabric filter for household wastewater treatment.

Conventional and modified membrane bioreactors (MBRs) are increasingly used in small-scale wastewater treatment. However, their widespread applications are hindered by their relatively high cost and operational complexity. In this study, we investigate a new concept of wastewater treatment using a nonwoven fabric filter bag (NFFB) as the membrane bioreactor. Activated sludge is charged in the nonwoven fabric filter bag and membrane filtration via the fabric is achieved under gravity flow without a suction pump. This study found that the biofilm layer formed inside the NFFB achieved 10mg/L of suspended solids in the permeate within 20 min of initial operation. The dynamic biofilter layer showed good filterability and the specific membrane resistance consisted of 0.3-1.9 x 10(12)m/kg. Due to the low F/M ratio (0.04-0.10 kg BOD(5)/m(3)/d) and the resultant low sludge yield, the reactor was operated without forming excess sludge. Although the reactor provided aerobic conditions, denitrification occurred in the biofilm layer to recover the alkalinity, thereby eliminating the need to supplement the alkalinity. This study indicates that the NFFB system provides a high potential of effective wastewater treatment with simple operation at reduced cost, and hence offer an attractive solution for widespread use in rural and sparsely populated areas.

Changes in mixed liquor and organic foulant properties affect membrane fouling for non-nitrifying and nitrifying biological conditions.

A submerged membrane bioreactor treated settled municipal wastewater at a non-nitrifying solids retention time (SRT) condition (2 days) and a nitrifying SRT condition (10 days), to determine the effect of nitrification on mixed liquor properties and membrane fouling. Membrane fouling rates were almost 10 times greater at the 2-day SRT compared with the 10-day SRT, and results showed increased concentrations of high-molecular-weight organic molecules at the 2-day SRT. The Fourier transform infrared spectroscopy (FTIR) results of the fouled membrane from the 2-day SRT exhibited strong peaks for carbohydrates, while the fouled membrane from the 10-day SRT did not. This is consistent with the fact that, although the total carbohydrate soluble microbial product concentration was highest at the 10-day SRT, the carbohydrate consisted of mostly low-molecular-weight (< 1 kDa) molecules, and 97% of this carbohydrate passed through the membrane at the 10-day SRT.

Fate and transport of endocrine-disrupting compounds (oestrone and 17beta-oestradiol) in a membrane bio-reactor used for water re-use.

Oestrogens have been detected in the effluents of sewage treatment plants (STPs) in several countries, as well as in surface water. This occurrence is fundamentally attributed to the excretion of oestrogen from humans and mammalian bodies, and the incomplete removal of these compounds from wastewater treatment plants. These micro-pollutants are causing great concern when it comes to water re-use. There is a lack information on endocrine-disrupting compounds (EDCs) such as oestrogen in water re-use systems, e.g. a membrane bioreactor (MBR). It is clear that there is a strong need for "EDCs in MBR for water re-use". This study examined an E1 and E2 biodegradation batch test by an activated sludge and hollow fibre membrane filtration test with and without a bio-cake. E2 was effectively removed, even in high initial concentrations (1,000 ppb). E2 was oxidised into E1, and E1 had a lower adsorption rate than E2. The membrane with the bio-cake provided better removal than the virgin membrane.

The effect of calcium on the membrane biofouling in the membrane bioreactor (MBR).

A continuous bench-scale submerged membrane bioreactor (BSMBR) was operated in two modes; low (LC) and optimum calcium (OC) concentrations, to investigate the effect of calcium on membrane biofouling. Both the cake layer and pore blocking resistances were reduced in the operation under OC conditions. In order to find the causes of fouling, molecular weight fractionations of the extracellular polymeric substances (EPS) and soluble microbial products (SMP) were conducted, and the relative hydrophobicity of the sludge, EPS and SMP were also measured. The reduction in the cake layer resistance was assumed to be due to the decrease of filamentous bacteria, and better flocculation caused by the calcium bridges and the increased hydrophobicity of EPS in the operation under OC conditions. It was suggested that the pore blocking resistance was reduced due to the low SMP rejection of the membrane and the fewer hydrophobic reactions of the SMP in the operation under OC conditions. Fourier-transform infrared analysis of the fouled membrane surface supported that proteins and carbohydrates were the main foulants during the BSMBR operation.