NOVELTY - A twin liquid-solid fluidized bed system (100), comprises a first fluidized bed (10) which is a riser bed including an inlet at its second end for introducing a first fluidizing fluid (20) into the bed; a second fluidized bed (30) which is a downer bed; first connecting conduit (52) connecting second end of first bed to first end of second bed, and including a device to feed solid bacteria coated particles (50) into second bed; second connecting conduit (54) connecting second end of second bed to first end of first bed; and a device to feed solid particles into beds through the conduits.    USE - As a twin liquid-solid fluidized bed system for biological nutrient removal in a raw wastewater feed stream to remove carbon, nitrogen and phosphorus (claimed); useful in municipal wastewater treatment application.    ADVANTAGE - Biological nutrient removal (BNR)-liquid-solid fluidized bed (LSFB) system can handle both soluble and particulate-laden wastewater, thus eliminating the need for primary clarifiers. The BNR-LSFB system achieves the simultaneous elimination of organic carbon, nitrogen, and phosphorus, in a very efficient manner and with very compact space requirements. A much smaller area and very compact reactor sizes, due to higher biomass density per unit bioreactor volume and the elimination of both primary and secondary clarifiers. The BNR-LSFB system provides the minimization of operational labor requirements with the elimination of routine tasks such as solids analysis in the aeration tank and the return of activated sludge, cleaning of clarifier weir launders, wasting sludge, control of chemical dosing and maintenance of chemical feed systems; an enhanced process stability as a result of better biosolids retention; less vulnerability to shock loadings of toxicants and inhibitory substances as a result of lower toxicant-to-biomass ratios than in suspended-growth; the minimization or elimination of chemical addition for phosphorus removal; a significant reduction in sludge generation and the minimization of chemical sludge compared to the activated sludge system due to lower bacterial yields in the anoxic tank, and the minimization of biological sludge compared to the suspended growth BNR system due to its operation at a much longer solids residence time and accordingly much higher biomass decay rates; a substantial reduction in oxygen requirements and thus major savings in energy requirements; and the potential reduction in organic carbon requirements for nutrient-removal due to enhanced utilization of particulate substrates as a result of better entrapment in the fluidized bed as well as decaying biofilm as a carbon source. The BNR-LSFB system has the capability to handle simultaneously soluble and particulate wastes due to the suspension of particulates within the fluidized-beds. The process offers the potential to achieve a highly treated effluent quality at significant cost savings in capital and operation/maintenance costs compared to existing technologies, with remarkable process stability. The fixed-film BNR LSFB process is applicable to any municipal wastewater treatment application, and also it is particularly advantageous for treatment of wastes from industries that very often have space limitations and special needs.    DETAILED DESCRIPTION - A twin liquid-solid fluidized bed system (100), comprises a first fluidized bed (10) having a first and second end, where the first fluidized bed is a riser fluidized bed including an inlet at the second end for introducing a first fluidizing fluid (20) into the first fluidized bed; a second fluidized bed (30) which is a downer fluidized bed having a first end and a second end; first connecting conduit (52) connecting the second end of the first fluidized bed to the first end of the second fluidized bed, where the first connecting conduit including a device to feed solid bacteria particles (50) into the second fluidized bed; second connecting conduit (54) connecting the second end of the second fluidized bed to the first end of the first fluidized bed; and a device to feed the solid bacteria coated particles into the second fluidized bed through the first connecting conduit and to feed the solid particles into the first fluidized bed through the second connecting conduit. The solid particles and second fluidizing fluid (40) flow in counter flow relationship in the second fluidized bed, and the solid particles and the first fluidizing fluid flow co-currently in the first fluidizing column. An INDEPENDENT CLAIM is included for a process for biological nutrient removal in a raw wastewater feed stream to remove carbon, nitrogen and phosphorus, involving flowing raw wastewater feed stream into a first fluidized bed and flowing a first fluidizing fluid into first fluidized bed and passing solid particles having effective immobilized bacteria coated and first fluidizing fluid through an anoxic zone maintained under anoxic conditions; circulating solid particles and first fluidizing fluid through an anaerobic zone maintained under anaerobic conditions in first fluidized bed; separating some of first fluidizing fluid from solid particles to form a recycle stream and circulating solid particles and a remaining amount of first fluidizing fluid into a second fluidized bed; circulating particles transferred to second fluidized bed with a stream of a second fluidizing fluid through second fluidized bed; and circulating solid particles from second fluidized bed to first fluidized bed along with a part of nitrified effluent and separating remaining nitrified effluent from solid particles in second fluidized bed and removing a portion of this separated nitrified effluent from system as treated effluent and recycling rest back into an inlet to second fluidized bed to form second fluidizing fluid.    DESCRIPTION OF DRAWING(S) - The figure shows a schematic diagram of a twin liquid-solid fluidized bed biological nutrient removal system.    First fluidized bed (10)    first fluidizing fluid (20)    Second fluidized bed (30)    Second fluidized fluid (40)    First connecting conduit (52)    Second connecting conduit (54)    Twin liquid-solid fluidized bed system. (100)