The Effectiveness of Aeration Recirculation in Controlling VOC Emissions from Publicly Owned Treatment Works

Abstract

The effects of aeration recirculation on oxygen transfer and the fate of five volatile organic compounds (VOCs) commonly found in publicly owned treatment works (POTWs) influent are studied using various modeling approaches. The five compounds are benzene, chloroform, methylene chloride, toluene, and trichloroethylene. The models predict that the overall oxygen transfer efficiency can be increased by 96.7% at 50% aeration recirculation with only a 9.6% drop in oxygen transfer rate. The emission reductions and biodegradation improvements are compound specific; for the compounds investigated here, about 40% emission reductions and 16% biodegradation increases can be achieved at 50% aeration recirculation. The temperature effect on the VOC fate mechanisms is also investigated. Overall, the model predictions reveal that up to 50% aeration recirculation is effective in controlling VOC emissions.     

IMMEDIATE CONTEXTUAL INFLUENCES ON MATERNAL BEHAVIOR: ENVIRONMENTAL AFFORDANCES AND DEMANDS

Although it is commonly recognized that parenting is multiply determined, mechanisms by which the context influences parental behavior have rarely been examined. In this paper, the role of environmental affordances and demands are described and tested in two observational studies. In Study 1, mothers and their 3-year-old children were observed in three settings where affordances and demands differed: the home, park, and laboratory. In Study 2, mothers and their children engaged in three laboratory conditions in which the amount of demands on the mother was manipulated. Several child-rearing variables showed systematic relations with the presence of affordances and demands. It is concluded that affordances and demands play an important role in influencing maternal behavior by acting as environmental cues for place-related behavior. Further, it is proposed that parental perceptions of the immediate context and the recognition of appropriate environmental cues are paramount in understanding the variability of parental behavior across situational contexts.     

Effects of UV-B radiation on the gills of Catla catla during early development

Scanning electron microscopic (SEM) study of gills of Catla catla catla (17-day-old) exposed to UV-B radiation (145?µW?cm^?2 at the water surface) for three different exposure times: 5, 10 and 15?min was conducted. Fish without UV-B exposure served as control. UV-B radiation damaged both gill filaments and lamellae. The intensity of damage was minimal in 5?min exposed fish, followed by 10?min exposed fish and maximal in 15?min. The gill epithelium was severely damaged in 15?min irradiated fish compared to control. Pavement cells (PVCs) were damaged and the numbers of microridges within PVCs decreased. The deep boundary of PVC was not clear. In some area of gill epithelium, PVCs were destroyed and mitochondrion-rich cells (MRCs) were exposed. The 5?min exposure reduced the number of microridges in the PVCs, but the boundary of PVCs was still visible. MRCs in the gill epithelium were not exposed in 5?min exposed fish. The damage to PVCs and subsequent exposure of MRCs in UV-B irradiated fish may hamper respiratory functions and disturb osmoregulation in catla.     

Acute toxicity of ammonia to a freshwater teleost,Labeo bata larvae

Ammonia toxicity tests were performed with Labeo bata (bata) larvae of three different size groups. One hundred percent survival of larvae (500.0?±?4.0?mg) was recorded when exposed to ammonia concentrations of 1.0–13.56?mg?L^?1 at 96?h of exposure. Bata larvae exposed to ammonia concentrations of 15.8–25?mg?L^?1 showed 10–74% mortalities. The 96?h LC₅₀ value for 200 (±5), 250 (±2) and 500 (±4) mg bata larvae were 11.5, 16.8 and 22.5?mg?L^?1 un-ionised ammonia concentrations, respectively. When fish were exposed to different doses of ammonia, behavioural changes immediately occurred even at the lowest dose. At first, the fish became hyperexcitable, the skin darkened and they showed an increased ventilation frequency, fish behaviour became normal, 24?h after exposure. A 96?h LC₅₀ value of un-ionised ammonia showed direct relationship with the increasing size of bata larvae.     

Removal of heavy metals using waste eggshell

The removal capacity of toxic heavy metals by the reused eggshell was studied.As a pretreatment process for the preparation of reused material from waste eggshell,calcination was performed in the furnace at 800℃for 2 h after crushing the dried waste eggshell.Calcination behavior,qualitative and quantitative elemental information,mineral type and surface characteristics before and after calcination of eggshell were examined by thermal gravimetric analysis(TGA),X-ray fluorescence (XRF),X-ray diffraction(XRD) and scanning electron microscopy(SEM),respectively.After calcination,the major inorganic composition was identified as Ca(lime, 99.63%)and K,P and Sr were identified as minor components.When calcined eggshell was applied in the treatment of synthetic wastewater containing heavy metals,a complete removal of Cd as well as above 99% removal of Cr was observed after 10 min. Although the natural eggshell had some removal capacity of Cd and Cr,a complete removal was not accomplished even after 60 min due to quite slower removal rate.However,in contrast to Cd and Cr,an efficient removal of Pb was observed with the natural eggshell rather than the calcined eggshell.From the application of the calcined eggshell in the treatment of real electroplating wastewater, the calcined eggshell showed a promising removal capacity of heavy metal ions as well as had a good neutralization capacity in the treatment of strong acidic wastewater.