Abstract: A process and an apparatus are disclosed for the monitoring and treatment of circulating water of open circulation systems, preferably in cooling tower circulation systems, in which at least one partial minor stream is continuously diverted from the main circulating water supply and directed through a compact module in which, in an automatic sequence, the pH value of the partial stream is measured and adjusted by the addition of any necessary acid, the conductivity of the partial stream is measured, preferably inductively, and an elutriation unit is activated to drain excessively conductive water, corrosion inhibitor is added to the partial stream in dependence upon the quantity of fresh water added to the circulating water, organic and/or inorganic biocides can be added and the partial stream is filtered and returned continuously to the main circulating water supply.

Abstract: A method and apparatus for reducing the NO.sub.x content of hot stack (exhaust) gas produced by a furnace burning a fossil fuel, comprising recycling part of said NO.sub.x -containing stack gas, in admixture with cold fresh air, back into the combustion chamber of the furnace.