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Sludge samples from an upflow anaerobic sludge blanket (UASB) reactor and four submerged aerated biofilters (BFs) of a wastewater treatment plant (1,000 inhab.) were processed at bench scale by alkaline and acid hydrolysis with the objective to evaluate the organic matter solubilization, volatile solids (VS) destruction and the effect of hydrolytic processes on the extracellular polymeric substances (EPS) fraction of the sludge samples. The results showed that alkaline hydrolysis of sludge samples treatment with 1.0% total solids (TS) using NaOH 20 meq L−1 was more efficient on organic matter solubilization and VS destruction than acid hydrolysis. The EPS sludge content was also affected by the alkaline treatment of anaerobic sludge samples. The EPS concentrations (mg EPS/gVSS) on the anaerobic sludge after the alkaline treatment were significantly lowered according to sample height in the UASB reactor. Data indicated that the EPS sludge fraction is the main component affected by the alkaline hydrolytic process of anaerobic sludge samples.

Duckweed based stabilization ponds, an alternative for wastewater treatment, are attracting a growing interest from researchers because they are basically a low cost technology, easy to built and operate, and produce tertiary quality effluents. Besides, this technology offers the possibility of resource recovery by producing high quality duckweed protein, which can be of further use. Since the technology is rather new, there are many aspects to be studied before its full-scale implementation. It is necessary to gain sound knowledge of the basic principles of the complex processes occurring in the system, as well as of the practical aspects of design and operation. The presence of a layer of duckweed on the surface is expected to produce different environmental and physicochemical conditions in the water from those found in conventional stabilization ponds. These environmental and physicochemical conditions affect both plant growth and biological treatment processes in the system, therefore it is important to determine their behavior in a duckweed system and how they can be affected by an anaerobic pretreatment. Continuous flow pilot plants composed of seven ponds in series were operated with artificial substrate under two different conditions: with anaerobic pretreatment and without anaerobic pretreatment. The flow was kept constant during the operation. Conditions such as pH, temperature, dissolved oxygen, alkalinity, conductivity, chemical oxygen demand, biochemical oxygen demand, total and ammonium nitrogen, nitrites and nitrates, and phosphorus were evaluated in the system under steady state conditions. The main conclusions from the study include the following: pH, temperature and oxygen profiles are more stable in duckweed ponds than in conventional stabilization ponds; anaerobic pretreatment has a significant effect on the oxygen concentration in the system and on the organic matter removal but not on the nutrient removal.