Control Of Water pH Research Articles

Desenvolvimento de um sistema para o controle do pH da água para microirrigação

O objetivo deste trabalho foi desenvolver um sistema eletrônico de controle do pH da água para microirrigação. O trabalho foi realizado no Laboratório de Hidráulica do Departamento de Engenharia de Biossistemas (LEB) da Escola Superior de Agricultura "Luiz de Queiroz" (ESALQ/USP). O sistema de controle consta de um sensor de pH, um circuito eletrônico programado para manter o pH da água em 5,5 e um dispositivo de injeção de ácido controlado por uma válvula solenóide comandada por pulsos elétricos enviados pelo circuito eletrônico. O sistema foi testado em águas de diferentes valores iniciais de pH (variando de 6,2 a 9,2) sob vazão constante (264 L h-1) e variável, sendo efetuada a medição do pH imediatamente à jusante do sistema e ao longo da linha lateral, nos pontos situados a 1, 14, 29 e 44 m do início e em diferentes intervalos de tempo a partir do início dos ensaios. Os resultados obtidos comprovam a eficiência do sistema para manter o pH da água na faixa desejada, tanto para a condição de vazão constante quanto para a variável. Não foram verificadas variações temporais nem espaciais significativas na linha lateral de irrigação.

Development of a Suppression Method for Corrosion of Carbon Steel by Double-Layer Ni Metal-Ni Ferrite Film

Water pH control or dissolved oxygen (DO) in water control is being applied to many thermal and nuclear power plants in order to reduce the corrosion of carbon steel (CS). In the former, a continuous pH adjuster, such as hydrazine, is injected into water during plant operation cycles, and in the latter, oxygen gas is injected into water and is controlled during plant operation. Then, we developed the Hitachi ferrite coating (Hi-F Coat) process to suppress the corrosion of CS in plant operation cycles without pH or DO control. In this process, a fine oxide film is formed on the CS base metal of the piping in solution at 363 K. In this study, we developed a method to form a double-layer Ni metal-Ni ferrite film to suppress the corrosion amount of CS in water. In this process, a double-layer film is formed on the base metal of the piping using four chemical reagents in solutions, Fe(HCOO)2, Ni(HCOO)2, H2O2, and N2H4 at 363 K. X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, and Auger electron spectroscopy measurements of the film show a close-packed double-layer thin film formed in the amount of 3.6 g/m2. The inner layer is mainly Ni metal and the outer layer is Ni0:7 2+Fe0:3 2+Fe2 3+O4. After adding the four chemical reagent solutions, Ni2+ ions were reduced on the CS surface and a Ni metal film was formed on the base metal. Then, a Ni0:7Fe0:3Fe2O4 film was formed on the CS surface by oxidation of Fe2+ to Fe3+ with H2O2. We confirmed that the respective corrosion amounts were reduced to 1/5 and 1/2 compared with those obtained without and with oxygen injection at 423 K. Furthermore, we analyzed the film after a corrosion test. The double-layer film changed to a Ni0:7Fe0:3Fe2O4 single-layer film. There is the possibility that the transformation from the double-layer film to the single-layer film reduced the corrosion of CS by preventing the diffusion of Fe ions from base CS to high-temperature water.

ファジィ制御による排水ｐＨ制御実施事例

王子板紙株式会社佐賀工場は，2系列の排水処理設備を有しており，1系列が古紙処理プラント排水を活性汚泥＋加圧浮上で処理し，もう1系列が抄紙プラント排水を活性汚泥＋凝集沈殿で処理し，工場西側を流れる福所江川に放流している。これらの排水処理設備には，排水pHの調整用にPID制御が7ループあるが，その制御性は決して満足いくものではなかった。一般的にpH制御の中和反応は非線形であり，更に排水プラントの場合は，pH計設置場所の制約によりむだ時間が長く，排水量変化によりむだ時間も変化する。従って，pH制御に時間をかけてPIDパラメーターをチューニングするがその結果は，あくまでもチューニング時の排水プラント状態における代表パラメータを求めているだけで，全てのプラント状態を満足できるものとはなっていない。本稿では，このpH制御7ループの内，制御性が悪く，かつ改善要求が強かった2ループにファジィ制御を導入し，排水流量やむだ時間の変動に対して非常に良好な制御性を示し，薬品費削減につながったことを報告し，併せて導入した2ループのファジィ制御の原理について報告する。

Removal of bromate ion from water using TiO2 and alumina-loaded TiO2 photocatalysts

The effects of pH and the surface charge of photocatalyst on photocatalytic reduction of bromate ions in water were examined by using TiO2 and alumina-loaded TiO2 photocatalysts. The amount of adsorbed bromate ion on TiO2 and the reduction rate of bromate ion by the TiO2 photocatalyst increased with lowering pH. It was suggested that the bromate ion adsorbed predominantly on the positively charged surface sites of TiO2 at lower pH, which thus promotes the rate of reduction. The iso-electric point of the TiO2 photocatalyst was shifted to the higher pH region by loading alumina on the TiO2 surface, which resulted in the increase of the adsorbed amount of bromate on the photocatalyst and the reduction rate of bromate ion by the photocatalyst at neutral pH. It was concluded from these results that the photocatalytic reduction of bromate ion can be promoted by pH control of water or by controlling the surface charge of the photocatalyst by loading alumina without pH control of water.

Effect of oxygenation, aeration and pH control on water quality and survival of turbot, Scophthalmus maximus (L.), kept at high densities during transport

The survival of turbot, Scophthalmus maximus (L.), kept at high densities (0.5 kg 1−1 water) was studied when O2 was added by oxygenation, aeration, a combination of oxygenation and aeration, or by aeration with control of water pH by the addition of acid. Oxygen instead of air increased the LT50 (lethal time for 50% of the population) from 40 h to 130 h. Aeration in combination with acid addition further increased LT50 to 220 h. The results show that the transport time of live fish can be increased by reducing pH, either by raising carbon dioxide levels or by adding acid, probably because of reduced toxicity of total ammonia (NH3 and NH4+). In all groups, mortality was recorded at NH3 concentrations above 0.4 mg 1−1 NH3-N.