Nitrogen removal in a shallow maturation pond with sludge accumulated during 10 years of operation in Brazil

Nitrogen dynamic in vitro using sludge of a sewage stabilization pond from Patagonia (Argentina)

A relevant and current aspect of wastewater treatment systems is related to the processes of the nitrogen cycle that results in its elimination in gaseous forms. In the present study, we report the first measurements of nitrate-reducing rate (NRR) at lab-scale, using the flow-through reactor technique with sludge of a sewage stabilization pond system located in Patagonia (Argentina). Sludge was collected from Inlet and Outlet areas, in winter and summer. The sludge was characterized by having high moisture content (>94%) and organic matter concentration greater than 37%. The nitrate reduction experimental dates fitted significantly to the Michaelis-Menten model, allowing the estimation of the parameters that regulate the NR kinetics. The maximum potential nitrate reduction rate (Rmax) showed great variability, registering a maximum of 131.6 μmol-N·gdw-1·h-1 (Outlet-Summer) and a minimum of 4.1 μmol-N·gdw-1·h-1 (Inlet-Winter). The lowest half saturation constant (Km) was recorded in the Inlet sludge during the winter (6.1 mg N-NO3-·L-1), which indicates a greater affinity for nitrate of this bacterial consortium. An unusually high activity of NR was registered, being higher with sludge from the Outlet zone and with summer temperature. In full-scale ponds, the NR activity could explain a relevant part of the nitrogen removal that involves the escape of gaseous forms.

The occurrence and role of Nitrospira in nitrogen removal systems

Application of the modern microbial techniques changed the paradigm about the microorganisms performing nitrification. Numerous investigations recognized representatives of the genus Nitrospira as a key and predominant nitrite-oxidizing bacteria in biological nutrient removal systems, especially under low dissolved oxygen and substrate conditions. The recent discovery of Nitrospira capable of performing complete ammonia oxidation (comammox) raised a fundamental question about the actual role of Nitrospira in both nitrification steps. This review summarizes the current knowledge about morphological, physiological and genetic characteristics of the canonical and comammox Nitrospira. Potential implications of comammox for the functional aspects of nitrogen removal have been highlighted. The complex meta-analysis of literature data was applied to identify specific individual variables and their combined interactions on the Nitrospira abundance. In addition to dissolved oxygen and influent nitrogen concentrations, temperature and pH may play an important role in enhancing or suppressing the Nitrospira activity.

Performance evaluation of a natural treatment system for small communities, composed of a UASB reactor, maturation ponds (baffled and unbaffled) and a granular rock filter in series

Post-treatment of anaerobic reactor effluent with maturation ponds is a good option for small to medium-sized communities in tropical climates. The treatment line investigated, operating in Brazil, with an equivalent capacity to treat domestic sewage from 250 inhabitants, comprised a upflow anaerobic sludge blanket reactor followed by two shallow maturation ponds (unbaffled and baffled) and a granular rock filter (decreasing grain size) in series, requiring an area of only 1.5 m² inhabitant^-1. With an overall hydraulic retention time of only 6.7 days, the performance was excellent for a natural treatment system. Based on over two years of continuous monitoring, median removal efficiencies were: biochemical oxygen demand = 93%, chemical oxygen demand = 79%, total suspended solids = 87%, ammonia = 43% and Escherichia coli = 6.1 log units. The final effluent complied with European discharge standards and WHO guidelines for some forms of irrigation, and appeared to be a suitable alternative for treating domestic sewage for small communities in warm areas, especially in developing countries.