Phosphate Adsorption and Recovery from an Industrial Wastewater

Phosphate is one of the major causes of the water eutrophication, because it is often the limiting nutrient for primary production in fresh water and marine. The world health organization (WHO) especially established the committee for this, in order to research its origin cause of formation and make the countermeasure. Phosphate removal from wastewater has been widely investigated. Consequently, the later research aim would tend to more competitive and economy. The utilization of industrial wastes or byproducts for phosphorous adsorption has been given a great attention. Those low cost adsorbents include fly ash, blast furnace slag , red mud , alum sludge , and other materials. This study presents adsorptive removal of phosphate by using adsorbent BT-1 containing iron oxide. It is a disposable byproduct which is produced by the fluidized-bed reactor Fenton (FBR-Fenton) crystallization technology. The source of the stock phosphate wastewater was obtained from the Al-etching procedure of a certain thin film transistor-liquid-crystal display (TFT-LCD) factory in Taiwan. This wastewater has complex contents, including PO4, Cl, NO3, SO4, and CH3COO, etc. Adsorption kinetics, ion effect, desorption, and pilot-scale test were examined in this work. The sample was air-dried and then sieved to give a 0.25~0.50 mm size using standard sieves. Before adsorbing, absorbent was under the pretreatment step. The phosphate solution (85 wt%, HPLC) was diluted in a proper time to different setting concentration. During adsorption process, 100 ml of phosphate solutions was treated with 5 g of BT-1 in several flasks respectively. Samples were kept for equilibration in a rotary flask shaker after 24 hours. The temperature and the stirring speed were kept at 305K and 100 rpm. During desorption process, 1g of modified BT-1 and 10g NaOH solution with different concentration were put in several flasks. All the other steps and conditions were done such like adsorption. After diluting in a proper time, samples were measured by ion chromatography analysis (IC, 732 IC Detector, A Supp 1 column, Metrohm). Adsorption kinetics shows that the BT-1 is a good adsorbent for adsorptive removal of phosphate. The equilibrium of adsorption curve presents that adsorption capacity increase with phosphate concentration increase. The unit adsorption capacity was grown extremely to 300 mg P/g BT-1 in a highly equilibrium concentration. Both chloride and nitride ion in the solution have less effective with phosphate adsorption. Sulfate and acetic acid ion has counter potential in phosphate adsorption. In the other hand, sulfate ion compete the activity site with phosphate ion, and organic compound can induce the capture of phosphate from solution. It was proved by adsorption capacity in industrial wastewater more than it in pure phosphate solution. From previous study, we had known that phosphate can be uptake from BT-1 in sodium hydroxide solution. Adding sodium carbonate in the solution can also enhance the desorption ability. We trialed a pilot-scale fixed bed to confirm the efficiency of scale up. The extended experiment recovered 74% of phosphate from BT-1 and got a recycle solution over 30 times of primary concentration. Due to the low cost and high adsorptive capacity, BT-1 has the potential to be an adsorbent in phosphate removal.