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2,4-Dichlorophenol used in the manufacture of pesticides, germicides, resins, seed disinfectants and antiseptics, if disposed untreated causes greater havoc for land and aquatic environment. In all the earlier works, 2,4-dichlorophenol has been fed along with easily biodegradable substrate, glucose as one of the constituents. A modi®ed 4-stage RBC was used for the biodegradation studies of 2,4-dichlorophenol. The micro organisms attached to the disks were specially acclimatised to the extent that the 2,4-dichlorophenol alone serves as the sole carbon source supporting their metabolic activities. The RBC was operated at 12 rpm. The toxic substrate removal studies were carried out in the hydraulic loading rates ranging from 0.005 m 3 /m 2 /d to 0.035 m 3 /m 2 /d and organic loading rates from 0.35 g/m 2 /d to 6.15 g/m 2 /d. A correlation plot between 2,4-dichlorophenol removal and organic loading rate is presented. A mathematical model is proposed using regression analysis. List of symbolsA m 2 total surface area of the discs D m Submerged disc depth F Removal of 2,4-dichlorophenol expressed as a fraction L gm A2 d A1 In¯uent organic loading Q m 3 m A2 d A1 hydraulic loading rate S mgl A1 In¯uent 2,4-dichlorophenol concentration W rpm rotational speed F hr hydraulic detention time T°C wastewater temperature 1 Introduction 2,4-dichlorophenol (DCP) is used extensively in the manufacture of herbicides, pesticides, resins and wood preservatives. DCP can be found in the environment in degraded herbicides, saw mills, wood waste incinerators and hazardous waste sites. DCP can cause death, respiratory failure, bone marrow atrophy and skin damage in animals and confers a bad taste and odour to food and water. Literature is available for biodegradation of different type of wastes ranging from domestic sewage, to industrial wastes like distillery, tapioca, sugar cane etc; using RBC technology. But very few reports are available for biological degradation of toxic phenolic waste wasters using RBC. Huang et al. (1985) studied the RBC treatment of phenol-formaldehyde resin waste waters. Pilot scale RBC's at various in¯uent phenol levels as high as 600 mg/l were used in this study. Results showed that average phenol removal rates were about 99 percent. Tokuz (1991) used RBC for studying the biodegradation of phenolic compounds such as 2-chlorophenol, 2,4-dichlorophenol, 2,4,6,-trichlorophenol; pentachlorophenol, 2-nitrophenol, diethyl phthalate and dibutyl phthalate. This study reveals that the phenolic compounds are biodegradable and RBC process is a viable process in treating phenolic waste waters. Radwan et al. (1997) used laboratory scale modi®ed RBC for studying the organic removal of 2,4-dichlorophenol waste waters. The concentration of 2,4-dichloropheonal treated was 200 mg/l and the removal ef®ciency was reported as 99.2%. In this study, DCP was spiked along with the synthetic sewage containing glucose as one of the constituents. The advantages of RBC is that, easy adaptability for small to medium type installations, sim...

The development of sorghum [Sorghum bicolor (L.) Moench] is influenced by genes that control sensitivity to photoperiod, and their interaction with photoperiod and temperature. While temperature influences development throughout the life cycle of plants, photoperiod influences the vegetative stage (from seedling emergence to panicle initiation). In order to simulate plant development, it is essential to know when sorghum plants first become sensitive to photoperiod, and how long that photoperiod sensitivity persists. Ten cultivars with different levels of photoperiod sensitivity were grown in pots under natural climatic conditions both in short days (SD: 8 h day-1) and long days (LD: 17 h d-l). Plants were transferred at different times after seedling emergence from SD to LD and vice versa. The time to panicle initiation (PI) for each transfer treatment was detemfined. In cultivars that remained continuously in SD, the time to PI varied from 16 to 27 d, whereas, in continuous LD it varied from 22 to 37 d. The cultivars started reacting to photoperiod 4-9 d after seedling emergence. After sensing photoperiod stimuli, inductive effects among cultivars persisted for 4-14 d in SD, and for 15-33 d in LD depending on their intrinsic photoperiod sensitivity. The sensitivity ended 2-5 d before panicle initiation. This interval, between completion of the photoperiod-inductive phase and the actual observation of PI under the microscope, represents the time required for the photoperiod-inductive stimulus to promote sufficient cell division and growth at the shoot apex for the morphological change to become visible as a shiny globular structure, We conclude that photoperiod sensitivity in these sorghum cultivars ends shortly before or at the PI stage. Our results support the assumptions followed in several crop simulation models that sorghum remains photoperiod-sensitive until the completion of the vegetative stage.

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