Natural zeolites as clinoptilolite may be used to recover wastewater ammonium, decrease the nitrogen content in the effluent from on-site sanitation systems and in wastewater treatment plants when nitrification-denitrification efficiency is low. The objective of this study was to estimate the ammonium adsorption capacity of clinoptilolite when being loaded with wastewater. Phosphorus and potassium sorption, ammonium desorption with tap water, and clogging were also studied. The study was performed by column experiments. Results of the investigation showed the ammonium adsorption capacity to increase with decreasing grain size, and the highest experimental adsorption capacity was 2.7 mg NH 4 -N/g. The breakthrough occurred immediately, probably due to a too high loading rate. Phosphorus and potassium sorption were minor. Of adsorbed ammonium, 23% was desorbed by tap water and desorption was more pronounced during saturated conditions. Filter clogging was extensive and probably caused by particles in the effluent wastewater and by microbiological growth.Résumé : Les zéolithes naturelles, tels que la clinoptilolite, peuvent être utilisées pour récupérer l'ammonium dans les eaux usées et diminuer l'effluent azoté des systèmes d'assainissement sur place et des usines de traitement des eaux usées lorsque l'efficacité de nitrification-dénitrification est faible. L'objectif de la présente étude était d'estimer la capacité d'adsorption d'ammonium de la clinoptilolite lorsque chargée avec des eaux usées. La sorption du phosphore et du potassium, la désorp-tion de l'ammonium avec l'eau du robinet, ainsi que l'encrassement ont également été étudiés. L'étude a été effectuée sur les colonnes. Les résultats de l'étude ont montré que la capacité d'adsorption d'ammonium augmente avec la diminution de la granulométrie et que la plus forte capacité d'adsorption expérimentale était de 2,7 mg NH 4 -N/g. La crevaison du filtre est survenue immédiatement, probablement en raison d'un taux de charge trop élevé. La sorption du phosphore et du potassium était mineure. De tout l'ammonium adsorbé, 23 % était désorbé par l'eau du robinet et la désorption était plus prononcée en conditions saturées. L'encrassement du filtre était généralisé et probablement causé par la présence de particules dans l'effluent d'eaux usées et la croissance microbiologique.

Three soil samples contaminated by chromated zinc arsenate (CZA) or chromated copper arsenate (CCA) were investigated in a laboratory scale to study As mobilization and to identify a chemical agent that could be used in soil washing to extract arsenic. Besides high As extraction, the cost, occupational health issues and technical aspects were considered when selecting the chemical. Arsenic is strongly bound to CZA/CCA soils; only ∼50% of the tot-As was removed from water-washed soils. High Fe or Al mobilization is not necessarily indicative of high As removal from CZA/CCA soils. A high Cu/As-ratio and a large amount of soluble Ca in the soil hampered As extraction. The high ratio can be an indication of stable Cu-arsenates in soil. Calcium can react with the extraction agent or with As during extraction. Sodium hydroxide, dithionite with citrate (and oxalate) (dithionite solutions), and oxalate with citrate were the most efficient chemicals for removing As from the soils. The disadvantages of using these strong chemicals are: a high cost (oxalate with citrate); damage to equipment (dithionite solutions); an adverse impact on occupational health (dithionite solutions); or a deterioration in soil quality after extraction (NaOH and dithionite solutons). Phosphate, solutions based on NH2OH·HCl, or citrate were not efficient in mobilizing As from the soils.

No abstract

Purpose Normal soil washing leave high residual pollutant content in soil. The remediation could be improved by targeting the extraction to coarser fractions. Further, a low/ high extraction pH and higher temperature enhance the pollutant removal, but these measures are costly. In this study, the utility of NaOH, oxalate-citrate (OC) and dithionite-citrate-oxalate (DCO) solutions for extracting of arsenic, chromium and zinc from contaminated soil were assessed and compared. In addition the effects of NaOH concentration and temperature on NaOH extractions, and those of temperature and pH on OC and DCO extractions, were evaluated. Materials and methods A two-level, full-factorial design with a centre point was implemented. Two factors, concentration and temperature,were evaluated in NaOH extractions, and pH and temperature for OC and DCO solutions. In all cases, the extraction temperature was 20°C, 30°C and 40°C. The studied NaOH concentrations were 0.05, 0.075 and 0.1 M. The pH in OC solutions was 3, 5 and 7, and in DCO solutions, 4.7, 6.3 and 6.7. Water-