Philip L. Sibrell

Evaluation of chemical coagulation–flocculation aids for the removal of suspended solids and phosphorus from intensive recirculating aquaculture effluent discharge

Abstract An evaluation of two commonly used coagulation–flocculation aids (alum and ferric chloride) was conducted for the supernatant overflow from settling cones used to treat the effluent from microscreen filters in an intensive recirculating aquaculture system. In addition to determining the effectiveness of these aids in removing both suspended solids and phosphorus, a systematic testing of the variables normally encountered in the coagulation–flocculation process was performed. Tests were carried out to evaluate the dosages and conditions (mixing and flocculation stirring speeds, durations, and settling times) required to achieve optimum waste capture. The orthophosphate removal efficiency for alum and ferric chloride were 89 and 93%, respectively, at a dosage of 90 mg/l. Optimum turbidity removal was achieved with a 60 mg/l dosage for both alum and ferric chloride. Both alum and ferric chloride demonstrated excellent removal of suspended solids from initial TSS values of approximately 100–10 mg/l at a dosage of 90 mg/l. Flocculation and mixing speed played only a minor role in the removal efficiencies for both orthophosphates and suspended solids. Both coagulation–flocculation aids also exhibited excellent settling characteristics, with the majority of the floc quickly settling out in the first 5 min.

Characterization of limestone reacted with acid-mine drainage in a pulsed limestone bed treatment system at the Friendship Hill National Historical Site, Pennsylvania, USA

Abstract Armoring of limestone is a common cause of failure in limestone-based acid-mine drainage (AMD) treatment systems. Limestone is the least expensive material available for acid neutralization, but is not typically recommended for highly acidic, Fe-rich waters due to armoring with Fe(III) oxyhydroxide coatings. A new AMD treatment technology that uses CO2 in a pulsed limestone bed reactor minimizes armor formation and enhances limestone reaction with AMD. Limestone was characterized before and after treatment with constant flow and with the new pulsed limestone bed process using AMD from an inactive coal mine in Pennsylvania (pH=2.9, Fe =150 mg/l, acidity =1000 mg/l CaCO3). In constant flow experiments, limestone is completely armored with reddish-colored ochre within 48 h of contact in a fluidized bed reactor. Effluent pH initially increased from the inflow pH of 2.9 to over 7, but then decreased to 6 during operation. Limestone removed from a pulsed bed pilot plant is a mixture of unarmored, rounded and etched limestone grains and partially armored limestone and refractory mineral grains (dolomite, pyrite). The ∼30% of the residual grains in the pulsed flow reactor that are armored have thicker (50- to 100-μm), more aluminous coatings and lack the gypsum rind that develops in the constant flow experiment. Aluminium-rich zones developed in the interior parts of armor rims in both the constant flow and pulsed limestone bed experiments in response to pH changes at the solid/solution interface.

Removal of phosphorus from agricultural wastewaters using adsorption media prepared from acid mine drainage sludge

Excess phosphorus in wastewaters promotes eutrophication in receiving waterways. A cost-effective method for the removal of phosphorus from water would significantly reduce the impact of such wastewaters on the environment. Acid mine drainage sludge is a waste product produced by the neutralization of acid mine drainage, and consists mainly of the same metal hydroxides used in traditional wastewater treatment for the removal of phosphorus. In this paper, we describe a method for the drying and pelletization of acid mine drainage sludge that results in a particulate media, which we have termed Ferroxysorb, for the removal of phosphorus from wastewater in an efficient packed bed contactor. Adsorption capacities are high, and kinetics rapid, such that a contact time of less than 5 min is sufficient for removal of 60-90% of the phosphorus, depending on the feed concentration and time in service. In addition, the adsorption capacity of the Ferroxysorb media was increased dramatically by using two columns in an alternating sequence so that each sludge bed receives alternating rest and adsorption cycles. A stripping procedure based on treatment with dilute sodium hydroxide was also developed that allows for recovery of the P from the media, with the possibility of generating a marketable fertilizer product. These results indicate that acid mine drainage sludges -- hitherto thought of as undesirable wastes -- can be used to remove phosphorus from wastewater, thus offsetting a portion of acid mine drainage treatment costs while at the same time improving water quality in sensitive watersheds.

Application of Chemical Coagulation Aids for the Removal of Suspended Solids (TSS) and Phosphorus from the Microscreen Effluent Discharge of an Intensive Recirculating Aquaculture System

Abstract An evaluation of two commonly used coagulation–flocculation aids (alum and ferric chloride) was conducted to determine optimum conditions for treating the backwash effluent from microscreen filters in an intensive recirculating aquaculture system. Tests were carried out to evaluate the dosages and conditions (mixing and flocculation stirring speeds, durations, and settling times) required to achieve optimum waste capture. The orthophosphate removal efficiency for alum and ferric chloride were greater than 90% at a dosage of 60 mg/L. Optimum turbidity removal was achieved with a 60-mg/L dosage for both alum and ferric chloride. Both alum and ferric chloride demonstrated excellent removal of suspended solids from initial total suspended solid values of approximately 320 mg/L to approximately 10 mg/L at a dosage of 60 mg/L. Flocculation and mixing speed and duration played only a minor role in the removal efficiencies for both orthophosphates and suspended solids. Both coagulation–flocculation aids ...

DEMONSTRATION OF A PULSED LIMESTONE BED PROCESS FOR THE TREATMENT OF ACID MINE DRAINAGE AT THE ARGO TUNNEL SITE, IDAHO SPRINGS, COLORADO 1

Pulsed limestone bed treatment is a new technology for the processing of acid mine drainage that utilizes limestone in fluidized bed reactors for an economical method of neutralizing acidity, adding alkalinity, and removing metal contaminants from mining impacted waters. The technology was developed by the U.S. Geological Survey, at the Leetown Science Center in Kearneysville, West Virginia. Previous demonstrations of this technology have taken place at coal mining sites in the Appalachian region. In this demonstration project, funded by the Mine Waste Technology Program of EPA, the Pulsed Limestone Bed (PLB) technology is being demonstrated at the Argo Tunnel Water Treatment Facility, which currently treats metal mining impacted waters flowing into Clear Creek. A 230 liter per minute pilot treatment system was installed in a moving van trailer and transported to the site in summer of 2004. Untreated water at the Argo site typically contains about 600 mg/L acidity (as CaCO3), due to the presence of hydrolysable metals including iron, aluminum, copper, zinc and manganese. Shakedown tests of the system were conducted by project cooperators from the Colorado School of Mines, and demonstrated an increase in pH from 3.0 to 7.0, nearly complete removal of iron and aluminum and an effluent alkalinity of about 100 mg/L as CaCO3. Post-treatment of the process effluent was required for removal of Mn and Zn, but test results indicated a decrease in reagent costs, as well as decreased sludge volume, due to the replacement of lime or sodium hydroxide by limestone as the neutralization agent. Complete process testing is scheduled for summer 2005.

Reducing Soluble Phosphorus in Dairy Effluents through Application of Mine Drainage Residuals

Three different dairy manure wastewater effluent samples were amended with mine drainage residuals (MDR) to evaluate the suitability of MDR for sequestration of phosphorus (P). Geochemical modeling of the manure wastewater compositions indicated that partially soluble P-bearing minerals including hydroxyapatite, octacalcium phosphate, and vivianite were all oversaturated in each of the manure wastewater samples. Initial MDR amendment test results indicated that these partially soluble P minerals suspended in the wastewater replenished P in the water phase as it was sorbed by the MDR samples. Further investigations revealed that the MDR samples were effective in decreasing soluble P when the amended manure was tested using the water-extractable P procedure. Under these conditions, up to 90 percent of the soluble P in the manure was converted to a sorbed, water-insoluble state. Water contamination and large-scale validation tests of the process were also conducted.

Comparison of sludge characteristics between lime and limestone/lime treatment of acid mine drainage

The U.S. Geological Survey, in cooperation with the Colorado School of Mines and the U.S. Environmental Protection Agency, has demonstrated the application of pulsed limestone bed (PLB) treatment of acid mine drainage (AMD) at the Argo tunnel discharge near Idaho Springs, Colorado. Current technology for AMD treatment at the Argo facility is neutralization with lime. However, lime neutralization often results in large amounts of highly hydrated metal oxide sludge, leading to high disposal costs. Use of the PLB process as a pretreatment typically offers cost savings not only through lower reagent costs, but also through decreased sludge volume. In this study we compared the characteristics of sludges created using lime only to a sludge that was pretreated with the PLB, followed by lime treatment. Lime treatment was performed batch- wise in a 60 gallon cone-bottom stirred tank where the pH was elevated to 10, and held for an hour. A sample of sludge from the operating treatment plant was also tested for comparison. The PLB/lime treatment was accomplished by first passing the water through the PLB system, followed by batch lime treatment to pH 10 as before. The sludge qualities were evaluated through settled sludge volume, filterability through a bench-scale filter press, and the moisture percentage in the filter cake. The PLB/lime treatment resulted in a decrease in sludge volume of 34% after 24 hours, with good filtration performance, and a final cake solids content of 22% versus 19% for the lime sludge. A decrease in lime consumption of 45% was also obtained with the PLB pretreatment.

TREATMENT OF METAL-MINE EFFLUENTS BY LIMESTONE NEUTRALIZATION AND CALCITE CO-PRECIPITATION 1

The U.S. Geological Survey - Leetown Science Center and the Colorado School of Mines have developed a remediation process for the treatment of metals in circumneutral mining influenced waters. The process involves treatment with a pulsed limestone bed (PLB) system, followed by co-precipitation of metal-carbonate impurities. The PLB system is resistant to armoring through the action of intermittently pulsing fluids through beds of limestone. This imparts significant alkalinity to the water, especially when CO2 has been added to enhance dissolution of the limestone. Then, product water is directed through an inclined channel containing limestone where co-precipitation of metal carbonates occurs, resulting in the removal of additional impurities, such as Zn, Cd and Mn. The maximum pH in the channel reaches 8.3, which is suitable for direct discharge into surface waters. The selectivity of the process results in lower reagent consumption and sludge volumes than would be expected with conventional lime or caustic treatment. The process was tested on four different hard-rock-mine-drainage effluents, and process performance and effluent composition were determined. If the water has only significant concentrations of zinc and minor concentrations of manganese, then removal of 90 % or more of the zinc is achieved. If the water has significant Mn concentration (≈ 50 mg/L) and minor Zn concentration, then removal of manganese is much more difficult and only after significant processing can the concentration of manganese be lowered to below 5 mg/L. Sludge volumes generated by the process are significantly smaller, only 10 % of those generated by hydroxide precipitation.