Precipitation of heavy metals by lime mud waste of pulp and paper mill

Precipitation of heavy metals in synthetic and actual wastewater with lime mud (solid waste generated from the pulp and paper production process) was experimented using Jar-tests. Separate synthetic wastewater samples were prepared for each of the following heavy metals: lead (1,433.7 mgPb2+/L), chromium (506.7 mgCr3+/L), cadmium (1,095 mgCd2+/L) and mercury (9.37 mgHg2+/L). The actual wastewater was tanning wastewater containing 74.49 mgCr3+/L and COD wastewater containing 683 mgHg2+/L. Adjustments of pH in the acidic range, pH 2-7, were made for each type of synthetic wastewater except for the Hg synthetic wastewater. The optimum conditions obtained from the tests of the synthetic wastewater were used for theactual wastewater samples. Precipitation of heavy metals with lime mud was effective as indicated by the removal efficiency as high as 90% up for Pb, Cd and Hg and 100% for Cr. However, the removal efficiency for the Hg-COD wastewater was only 67%. The precipitating pH was in the range of 10 up, which is the common pH range for metal carbonate precipitation. The optimum dosage of lime mud for Pb, Cr, Cd and Hg synthetic wastewater was 0.4-1.0 g/L, 2.0-4.0 g/L, 1.6-2.0g/L and 0.8 g/L, respectively. While the optimum dosage of lime mud for precipitating chromium in tanning wastewater was 3.8 g/L and 3.6 g/L for precipitating mercury in COD wastewater

Water Quality Simulation and Dissolved Oxygen Change Scenarios in Lam Takhong River in Thailand

Dissolved oxygen (DO) in Lam Takhong River gradually reaches zero value during the dry season on several occasions in the past decade causing the unsuitable quality for use as the raw water for Nakhon Ratchasima Town. Discharges of point sources and diffuse sources containing pollutants with organics and nutrients are the major cause of water quality deterioration in the river. To find the sources of impact on the water quality in the river, a one- dimensional steady-flow systems river water quality model, QUAL2Kw, was constructed and simulated. The model was calibrated and validated using the water quality data from 2008 to 2017 for the Lam Takhong River by seven monitoring stations. The modelling was applied to simulate various water quality parameters during the critical period to compare to the designated surface water quality criteria third class in Thailand (minimum dissolved oxygen at or above 4 mg/L; maximum biochemical oxygen demand (BOD), nitrate-nitrogen, and ammonia-nitrogen at or below 2.0, 5.0 and 0.5 mg/L, respectively). The study reach of the river flows 122 km from Lam Takhong Dam to the Mun River at Chaloem Phra Kiat district through the urban central area. Several segments of the river have been alarmed for many constituents with the dissolved oxygen impairment is the focus of the study. The scenarios of loads and upstream dissolved oxygen modification were conducted to assess the change of dissolved oxygen concentration. The result of the QUAL2Kw model showed that the decomposition of organic matter and a poor reaeration were the primary cause of the impairment. The local oxygenation causes fluctuations in dissolved oxygen levels along the river and the dissolved oxygen concentration decreases downstream of the river with some values fell the meet the fourth class of surface water quality criteria in Thailand (DO above 2 mg/L and BOD5<4 mg/L). The QUAL2Kw model is suitable for simulating the current and future river water quality and help water resources managers to issue the appropriate policy options for the Lam Takhong River