Treatment of phenanthrene and benzene using microbial fuel cells operated continuously for possible in situ and ex situ applications

Bioelectrochemical systems could have potential for bioremediation of contaminants either in situ or ex situ. The treatment of a mixture of phenanthrene and benzene using two different tubular microbial fuel cells (MFCs) designed for either in situ and ex situ applications in aqueous systems was investigated over long operational periods (up to 155 days). For in situ deployments, simultaneous removal of the petroleum hydrocarbons (>90% in term of degradation efficiency) and bromate, used as catholyte, (up to 79%) with concomitant biogenic electricity generation (peak power density up to 6.75 mWm−2) were obtained at a hydraulic retention time (HRT) of 10 days. The tubular MFC could be operated successfully at copiotrophic (100 ppm phenanthrene, 2000 ppm benzene at HRT 30 days) and oligotrophic (phenanthrene and benzene, 50 ppb each, HRT 10 days) substrate conditions suggesting its effectiveness and robustness at extreme substrate concentrations in anoxic environments. In the MFC designed for ex situ deployments, optimum MFC performance was obtained at HRT of 30 h giving COD removal and maximum power output of approximately 77% and 6.75 mWm−2 respectively. The MFC exhibited the ability to resist organic shock loadings and could maintain stable MFC performance. Results of this study suggest the potential use of MFC technology for possible in situ/ex situ hydrocarbon-contaminated groundwater treatment or refinery effluents clean-up, even at extreme contaminant level conditions

Inhibition of Nitrite Oxidation During Nitrification: Some Observations

Abstract A series of laboratory experiments were performed under controlled pH conditions and at room temperature to quantitatively study the inhibitory effects on Nitrobacter during nitrification. The results indicated that, in addition to the free ammonia (FA) concentration, the pH itself played an additive role in the inhibition of Nitrobacter. Reactors which were maintained at the same FA concentrations but at different pH levels exhibited different inhibition characteristics. It was also found that the acclimatization of Nitrobacter for an extended period of time may increase its FA tolerance limit from 0.1–1.0 mg/L cited in literature to 2.5 mg/L. Laboratory units containing less biomass (about 1000 mg/L) were more sensitive to FA inhibition than those with a higher concentration (1500 mg/L). A new concept of “recovery time” was introduced in this study to describe the microbial behaviour under inhibited conditions. The recovery time of Nitrobacter was found to depend on FA concentration, pH, time of exposure and biomass concentration.</jats:p

Gendered moral rationalities in later life: grandparents balancing paid work and care of grandchildren in Australia

AbstractIn recent years there has been increasing policy focus on keeping mature-age people engaged in the labour market. At the same time, grandparents play an important role as regular child-care providers for many families. Yet, little research has explored how grandparents negotiate these dual, often competing demands of paid employment and intergenerational care. Drawing on focus groups with 23 grandparents and an online survey of 209 grandparents providing regular child care for their grandchildren in Australia, this paper addresses this gap in the literature by examining how Australian grandparents experience and negotiate competing responsibilities as older workers and intergenerational care providers. The paper draws on the concept of gendered moral rationalities to examine the way in which grandparents’ decisions about participation in paid work are deeply embedded in idealised forms of parenting and grandparenting that are highly gendered. The paper suggests that, as the rate of both maternal and mature-age participation in the paid labour market continues to rise, inadequate attention is being paid to how time spent undertaking unpaid care is compressed, reorganised and redistributed across genders and generations as a result.</jats:p