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.

É sabido que a produção de resíduos industriais constitui uma das principais formas de degradação do meio ambiente. As indústrias têm empreendido um esforço crescente para tornarem seus processos produtivos menos agressivos, especialmente no que se refere à geração e gestão de resíduos sólidos. O objetivo desta pesquisa consistiu em estudar a geração de resíduos sólidos no processo produtivo de uma indústria automobilística, visando a apresentação de ações de redução. O estudo se deu por meio de observações in loco, registros fotográficos e cálculos da quantidade de resíduos sólidos gerados no processo de Moldagem e Acabamento em Plástico Reforçado com Fibra de Vidro. Constatou-se que a moldagem do tipo aberta, adotada pela fábrica, representa a principal fonte de geração de resíduos. Outra fonte refere-se ao desperdício de materiais, atribuído à falta de capacitação e de Educação Ambiental. Concluiu-se que a migração para um processo mais limpo e a adoção de um Programa de Educação Ambiental devem ser consideradas pela unidade fabril estudada.

This paper shows the performance of a baffled facultative pond for the treatment of piggery wastes. The full-scale system is composed of an equalizer, one decanter (DP), two anaerobic ponds (LA1 and LA2), one facultative pond (LF), with five baffles, and one maturation pond with water hyacinths (LAG). The studies were conducted over a 12 month period in the west region of Santa Catarina, Brazil. The system was supplied daily with a volume of 3 m3/day of farm wastes. A good performance of the treatment system was obtained with average removal efficiencies of 98% for chemical oxygen demand, 93% for total solids, 98% for total phosphorus, 92% for total nitrogen, 7 log units of faecal coliforms and 5 log units of total coliforms. The facultative pond performed well, removing 43% of the chemical oxygen demand, 47% of total nitrogen and 54% of total phosphorus. It was found that the first baffle in the facultative pond was mainly responsible for the efficiency of this pond, and compared with another study the introduction of the baffles improved the removal efficiency by 20% for total phosphorus.

Stabilization ponds used for the treatment of piggery wastes accumulate sludge over time, which is commonly used in agriculture. The objective of this study was to evaluate the agronomic potential of this kind of sludge. The samplings were collected in two different phases. The first in two anaerobic ponds (AP1 and AP2) and in one facultative pond with 5 transverse baffles and, the second in the same facultative pond with aeration. The removed sludge of AP1 and AP2 was characterized as rich sludge in volatile solids and with low stabilization, there was a great accumulation of the total phosphorus in the sludge of AP2. The facultative pond presented greater retention of nutrients in the sludge in relation to the anaerobic ponds. The annual accumulation of sludge was 13.3 cm/year in the AP1 and 6.70 cm/year in the AP2, while in the pond with aeration this was on the average of 0.5 cm/year, due to the aeration regime. The sludge can be used as a fertilizer in agriculture, if the chemical characteristics of the soil are taken into account so as to avoid the accumulation of nutrients and damage to plants.

Resumo: A produção de compósitos de plástico reforçado com fibra de vidro (PRFV) pode implicar em sérios danos à saúde do trabalhador e/ou ao meio ambiente devido, principalmente, à geração de aparas de processo e às emissões sonoras e atmosféricas. Neste sentido, este artigo teve como objetivo estudar as principais implicações do processo de Moldagem e Acabamento em PRFV em uma indústria automobilística sobre o meio ambiente e a saúde do trabalhador. Constatou-se que a moldagem aberta, processo adotado pela fábrica estudada, é a principal responsável pela geração de resíduos e que a perda de matérias-primas na forma de aparas pode chegar a 30%. Essas aparas, que representam 45% de todos os resíduos gerados pela fábrica, têm como destino final o aterro industrial. Constatou-se, ainda, que devido ao uso de moldes abertos os níveis de estireno e de "pó de fibra" se encontravam acima dos limites de tolerância representando riscos à saúde do trabalhador. Sendo assim, não apenas a empresa estudada como também outras em situações semelhantes precisam considerar a possibilidade da adoção de tecnologias menos agressivas, como aquelas que usam moldes fechados. A redução dos impactos negativos dos processos produtivos em sua fonte geradora precisa fazer parte da política das empresas. A prevenção deve ser contínua e melhorada a cada dia. Palavras-chave:Resíduos industriais. Saúde do trabalhador. Plástico Reforçado com Fibra de Vidro. Indústria automobilística. Abstract:The production of fiberglass reinforced plastic composite parts may cause serious damages to the health of workers and/or the environment, especially due to the generation of process trimmings, noise level and gas emission. In view of that, this essay aims at assessing the main impacts of the Molding and Finish processes of an automotive plant on the environment and occupational health. It was observed that the open molding method adopted by the studied plant is the main cause of the generation of residues and that the waste of raw materials as trimmings may reach up to 30%. The final destination of those trimmings, which represent 45% of all the residues generated by the factory, is the industrial landfill. It was also observed that, due to the use of open molds, the levels of styrene and fiber dust were above the tolerance limits, presenting risks to the health of the workers. Therefore, the studied company should consider the possibility of adopting less aggressive technologies, such as that used in closed molds. The reduction of the negative impacts of the productive processes in their source should be part of the company's policy. Furthermore, the prevention must be continuous and improved every day.