Computational fluid dynamics simulations of membrane filtration process adapted for water treatment of aerated sewage lagoons

The aim of this study is to apply the membrane bioreactor technology in an oxidation ditch in submerged conditions. This new wastewater filtration process will benefit rural areas (<5,000 population equivalent) subject to chronic water shortages by reusing this water for irrigation of green areas. For this purpose, the membranes developed without support are immersed in an aeration well and work in suction mode. The development of the membrane without support and more precisely the performance of spacers are approached by computational fluid dynamics in order to provide the best compromise between pressure drop/flow velocity and permeate flux. The numerical results on the layout and the membrane modules' geometry in the aeration well indicate that the optimal configuration is to install the membranes horizontally on three levels. Membranes should be connected to each other to a manifold providing a total membrane area of 18 m². Loss rate compared to the theoretical throughput is relatively low (less than 3%). Preliminary data obtained by modeling the lagoon provide access to its hydrodynamics, revealing that recirculation zones can be optimized by making changes in the operating conditions. The experimental validation of these results and taking into account the aeration in the numerical models are underway.

The Potential Role of Water Hyacinth in Wastewater Treatment in Nepal

River pollution is one of the significant environmental problems in Nepal. It is primarily due to the direct discharge of sewage from semi-urban and urban areas. The situation is widespread in Kathmandu Valley where the few wastewater treatment facilities are either inefficient or abandoned and modern wastewater treatment facilities are too expensive. The water hyacinth is known as the world’s most unwelcomed flora due to its invasive nature. However, numerous studies revealed many beneficial aspects of the plant species. The plants have already been widely used for different purposes like composting, substrate for mushroom farming, nutritious food for cattle, feed for biogas generation, protein synthesis, fibres for furniture, and for wastewater treatment, etc.This study investigates the possibility of water hyacinths in wastewater treatment in Nepal. Concentration reduction in BOD5, TN, TP, FC were analyzed weekly for four weeks, and the reduction efficiencies compared with systems without water hyacinth. The experiment resulted in a clear reduction of pollutants/nutrients in the water hyacinth treatment system compared to the system without water hyacinth. In addition, the water hyacinth treatment system was able to remove odour and colour completely, which made the system comparatively advantageous over the system without water hyacinth. It will be beneficial to upgrade existing sewage lagoons in Nepal into water hyacinth systems.DOI: http://dx.doi.org/10.3126/hn.v10i0.7101 Hydro Nepal Vol.10 January 2012 36-41

Late-Summer Feeding and Migration Behaviour and Numerical Trends of Common Nighthawks, Chordeiles minor, near Pinawa, Manitoba, 1976-2009

Feeding concentrations of Common Nighthawks, Chordeiles minor, during the evening in late summer were observed and counted near the Pinawa, Manitoba, sewage lagoons during 28 of the 34 years from 1976 to 2009. Counts were frequent but non-systematic in 1976-1981, infrequent in 1982-1991, and both frequent and systematic in most years during the period 1992-2009. Results of 226 counts are analysed and interpreted as showing a major decline in the local breeding population during the 1980s but more stable numbers of transient birds, assumed to originate farther north. The timing and other characteristics of feeding and migratory behaviour are discussed. The limitations of interpreting data from a single location are acknowledged and some systematic survey methods are recommended, emphasizing the importance of all-round, long-range visibility to help distinguish between migration and foraging.