(flow-rate 1 l min−1), then passed successively through
a tungsten heater and a degassing column packed with
plastic rings (Zhenhua Electric Industreatment Co., Ltd.,
China). For water quality control, temperature and
dissolved oxygen (DO) were measured daily, and
weekly measurements were made of total ammonium,
nitrite and pH levels using the Hach kit model DREL
2400 (Hach Company, Colorado, USA). The level of
dissolved oxygen was maintained above 6 mg l−1 by an
air pump (ADP-2200, Jinlai Pump Factory, China).