Phosphate biological reduction

Another actinide that has attracted attention is the mobile and long-lived a-emitter Np which is present in low-activity nuclear wastes. Removal is ineffective when using chemical-based techniques, but biotreatment of Np was possible using a combination of the biological reduction of Np(V) by S. putrefaciens followed by precipitation of Np(IV) phosphate by a Citro-bacter sp. (Lloyd et al. 2000). 

In sulfate-dominated wetlands, production of sulfide (through biological reduction of sulfate) and formation of ferrous sulfides may preclude phosphorus retention by ferrous iron in regulating phosphorus bioavailability (Caraco et al., 1991). In iron- and calcium-dominated systems, Moore and Reddy (1994) observed that iron oxides likely control the behavior of inorganic phosphorus under aerobic conditions, whereas calcium phosphate mineral precipitation governs the solubility under anaerobic conditions. This difference is in part due to a decrease in pH under aerobic conditions as a result of oxidation of ferrous iron compounds, whereas an increase in pH occurs under anaerobic conditions as a result of reduction of ferric iron compounds. The juxtaposition of aerobic and anaerobic interfaces promotes oxidation-reduction of iron and its regulation of phosphorus solubility. 

The destiny of most biological material produced in lakes is the permanent sediment. The question is how often its components can be re-used in new biomass formation before it becomes eventually buried in the deep sediments. Interestingly, much of the flux of phosphorus is held in iron(lll) hydroxide matrices and its re-use depends upon reduction of the metal to the iron(ll) form. The released phosphate is indeed biologically available to the organisms which make contact with it, so the significance attributed to solution events is understandable. It is not clear, however, just how well this phosphorus is used, for it generally remains isolated from the production sites in surface waters. Moreover, subsequent oxidation of the iron causes re-precipitation of the iron(lll) hydroxide floes, simultaneously scavenging much of the free phosphate. Curiously, deep lakes show almost no tendency to recycle phosphorus, whereas shallow... 

Points of Chemical Addition In independent physical-chemical treatment or in phosphate removal in the primary clarifier ahead of biological treatment, chemicals are added to raw sewage. In tertiary treatment for phosphate removal and suspended solids (SS) reduction, they are added to secondary effluent. In both cases, proper mixing and flocculation units are needed. For phosphate removal or improvement of SS capmre in biological secondary treatment, chemicals are often added directly to aeration units or prior to secondary settling units, without separate mixing and flocculation. In some phosphate removal applications coagulants are added at... 

Figure 17.8 The biologi-cal oxidation of an alcohol (sn-glycerol 3-phosphate) to give a ketone dihydroxy-acetone phosphate). This mechanism is the exact opposite of the ketone reduction shown previously in Figure 17.4.

The aldehyde intermediate can be isolated if 1 equivalent of diisobutvl-aluminum hydride (D1BAH) is used as the reducing agent instead of LiAlH4. The reaction has to be carried out at -78 °C to avoid further reduction to the alcohol. Such partial reductions of carboxylic acid derivatives to aldehydes also occur in numerous biological pathways, although the substrate is either a thioester or acyl phosphate rather than an ester. 

The first step in the biological degradation of lysine is reductive animation with a-ketoglutarate to give saccharopine. Nicotinamide adenine dinucleotide phosphate (NADPH), a relative of NADH, is the reducing agent. Show the mechanism. 

The biological function of the pentose phosphate cycle involves the production of two compounds NADP H2, which is a reductive force in the synthesis of various materials, and the metabolite ribose... 

The oxidation of 1,2- and 1,4-dihydropyridines has been extensively studied. This is due in large part to the occurrence of the 1,4-dihydropyridine ring system in the reduced forms of the coenzymes nicotinamide adenine di- and tri-phosphate (NADH and NADPH). These redox couples are responsible for a number of biological oxidations and reductions (B-70MI20701). 

---