Reclaimed wastewater quality enhancement by oxygen injection during transportation

摘要

In-sewer treatments have been studied in sewer systems, but few have been carried out onnreclaimed wastewater systems. A study of oxygen injection has been performed in a completelynfilled gravity pipe, 0.6 m in diameter and 62 km long, in cast iron with concrete inside coating,nwhich is part of the reclaimed wastewater reuse scheme of Tenerife (Spain). A high pressurenoxygen injection system was installed at 16.0 km from pipe inlet and a constant dosage ofn30 mg/L O2 has been injected during six months, under three different operational modesn(low COD, 63 mg/L; high COD, 91 mg/L; and partially nitrified water). Oxygen has been consumednin nitrification and organic matter reduction. Generally, nitrification is clearly favored instead ofnthe organic matter oxidation. Nitrification occurs, in general, with nitrite accumulation due to thenpresence of free ammonia above 1 mg/L. Denitrification is in all cases incomplete due to anlimitation of easily biodegradable organic matter content, inhibiting the appearance of anaerobicnconditions and sulfide generation. A notable reduction of organic matter parameters is achievedn(TSS below 10 mg/L), which is significantly higher than that observed under the ordinary transportnconditions without oxygen. This leads to a final cost reduction, and the oxygen injection systemnhelps water reuse managers to maintain a final good water quality in the case of a treatmentnplant malfunction.