This work concerned the application of anaerobic ponds for the primary treatment of urban wastewater in a Mediterranean climate. It was carried out on anaerobic ponds at large scale in Mèze (France). The anaerobic ponds constitute a good primary treatment with the removal of 55% of SS and 30% of BOD5, with a small surface area. The accumulation rate of sludge was only 0.017 m3/capita.year, due to their intensive anaerobic degradation. The anaerobic digestion reached equilibrium after one year of operation. The accumulation of sludge then showed seasonal variations with a substantial accumulation in winter and the digestion of the stock in summer. This change can be related to the influence of the temperature on methanogenesis. The production of biogas (83% CH4) was measured by gas collectors especially developed for this study and was also strongly dependent on temperature. The mass balance of carbon showed that 74% of the removed organic carbon was converted into CH4, 13% into dissolved inorganic carbon and 15% was stored in sludge. However, the anaerobic ponds presented a risk of creating odor nuisances with the emission of H2S.

This work was developed in two stages: initially in water hyacinth ponds under batch conditions (pilot-scale) and later in full-scale ponds under a continuous state, so as to determine local parameters for the operation of this kind of pond for piggery wastes treatment. Seasonal variations are important features influencing plant productivity and performance. The water hyacinth ponds were able to remove around 50% of the applied organic loads (COD, BOD, TN, TP), even in case of elevated values (110 kg/ha/day) applied for total nitrogen surface loads. An hydraulic retention time of 20 days was shown to be ideal for the treatment. The utilization of water hyacinths as a complement for the animal diet closes the productive cycle in a sustainable way. The results have demonstrated the feasibility of the proposed treatment system.

According to national statistical data, only 10% of the Brazilian urban population have their sewage treated. In the rural areas, where people usually treat sewage trough septic tank systems, this value is not greater than 5%. This situation, therefore, depicts a lack of basic sanitation in Brazil, which, in turn, is responsible for the utilisation of individual systems for the treatment of sewage by more than 100 million people. Generally, soils and water rivers are, no longer, the last fate for the discharged effluents. Wetland system for the treatment of domestic sewage have been employed in different situations and arrangements (combined system) always showing outstanding performances. The reasons which qualify this system for the treatment of effluents have been attributed to its low cost, easy maintenance and operation. The experiment was carried out in the Agriculture Secretary's Training Center, Santa Catarina State, responsible for servicing approximately 66 people daily, and was fed with local effluent. This work assesses the efficacy of such a kind of system, which is composed of a septic tank followed by the root zone, in the treatment of liquid effluents.

This work deals with studies on high-rate ponds, a batch working system that is followed by a filter pond where Chinese carp were introduced for piggery wastes treatment. COD removal values for the high-rate pond were in the order of 95% in the summer and 70% in the winter for an initial concentration of 2000 mg/L. Total nitrogen removal values ranged between 90% and 60%, respectively, in summer and winter periods for an initial concentration of 600 mg/L. Seasonal variations, which are mainly observed under differences of temperature, were shown to be not relevant for total phosphorus removal, a process that appears to depend mainly on increases of pH values over 8.5. An hydraulic retention time ranging between 15 to 20 days was found to be best for pond functioning. The plug flow model fits well to the pond's physical characteristics. The filter pond was shown to be a great potential process for removal of algae produced in the high-rate pond.

No abstract

O óxido nitroso (N2O) é altamente impactante ao meio ambiente por ser um dos três gases mais importantes quando considerado o alto potencial de efeito estufa e a baixa quantidade emitida para a atmosfera. A preocupação com a geração de N2O no tratamento de efluentes tem crescido nas duas últimas décadas. Muitos estudos vêm sendo realizados com o objetivo de avaliar as condições de geração e emissão de N2O em etapas de remoção de nitrogênio no tratamento, tanto em escala laboratorial quanto em estações de tratamento de efluentes. Essas pesquisas demonstram que, sob certas condições, ambos os processos podem produzir e emitir grandes quantidades de N2O para a atmosfera, o que remete à importância de mais investigações para determinar as condições específicas que minimizem a produção e a emissão de N2O nesse caso.

This work investigates the optimal management of water hyacinth ponds for the improvement of piggery waste treatment. The optimal harvesting strategy for the water hyacinth was studied using a single mathematical model. The water hyacinth optimal harvesting problem was formulated as an optimal control problem that was solved by application of Pontryagin's Maximum Principle. The optimization of the water hyacinth control in the pond indicates that the plant density should be reduced whenever it reaches half of the maximum capacity for growth. Two experimental systems were used to validate the mathematical model, one in real scale and the other in pilot scale. The results demonstrated the feasibility of the proposed harvesting strategy. For example, a comparison of the total nitrogen removal in the different pilot ponds confirmed the modeling results, in that the performance of the pond maintained with 50% water hyacinth cover was better than the others.

In this study, the problems provoked by nitrification of wastewater with low alkalinity were analyzed in a pilot sequencing batch activated sludge reactor (SBR)