Academic literature on the topic 'Filtrate recirculation'

AbstractThe bleaching sector of the wood pulp industry is its largest effluent generator. The aim of this study was to reuse the bleaching filtrate in order to reduce water consumption. The experiment was conducted by simulating the D0(EP)D1 bleaching sequence and recirculating different amounts of filtrate from the oxidation stage to control the pulp consistency of the delignification stage (pre-O). Physical, mechanical, chemical and optical properties of the pulp were studied. The accumulation of the non-process elements (NPE) and their effects were evaluated with the Aspen-Plus® computer simulator. The results of the computational modeling were satisfactory. The recirculation of filtrates increased the saturation index of the system by 19 %, but remained at sub-saturation levels. The pulp viscosity and elongation remained statistically stable. Recirculation of up to 50 % of the filtrate did not produce differences in pulp brightness; however, there were slight losses in the pulp resistances. In order to maintain 84 % ISO brightness, there was a higher consumption of the bleaching reagents. Up to 50 % of recirculation of the filtrates was accomplished without jeopardizing the system and the pulp quality and resulted in a savings of 55 m3 h−1 of water – 7 % of the consumption of the entire mill.

The model of an anaerobic bioreactor in which the basic biochemical reactions under the influence of an acting atmospheric precipitation, technological modes recirculation of a filtrate and participation of alive substance is developed transform a file of waste products in three phase system (gas, a liquid and firm substance).

The MUC (Montreal Urban Community) treatment plant produces approximately 270 tons of dry sludge daily (270 tds/day) during the physico-chemical treatment of wastewater. Recently, this treatment plant endowed a system of drying and granulation of sludge for valorization as an agricultural fertilizer having a capacity of 70 tds/day (25% of the daily sludge production). However, the metal content (mainly Cu and Cd) of the sludge surpasses the norms for biosolids valorization. In order to solve this problem, a demonstration project, from the lab scale to the industrial pilot plant, was carried out to test the Metix-AC technology for the removal of metals. A strongly metal-loaded filtrate was generated during the sludge decontamination. Tests concerned the study of the metal recovery by total precipitation and selective precipitation, as well as the use of alternative products for the metal precipitation. Other works consisted to simulate the acid filtrate recirculation from the decontaminated sludge (25% of the total volume) in the untreated sludge (75% of the total volume) intended for the incineration. The total precipitation with hydrated lime appeared effective for the recovery of metals (87% Cd, 96% Cr, 97% Cu, 98% Fe, 71% Ni, 100% Pb, 98% Zn). However, this option entails the production of an important quantity of metallic residue, which should be disposed of expensively as dangerous material. The selective iron precipitation does not appear to be an interesting option because the iron in solution within the leached sludge was principally present in the form of ferrous iron, which cannot be precipitated at pH lower than five. On the other hand, the use of commercial precipitating agents (TMT-15, CP-33Z, CP-NB and CPX) without pH adjustment of filtrate gave good results for the recovery of Cu and, to a lesser degree for the recovery of Pb. However, the efficiency for the other metals' (Cd, Cr, Fe, Ni and Zn) recovery was weaker (< 25%). Finally, the acid filtrate recirculation containing solubilised metals in untreated sludge destined for incineration appears to be the most interesting option. Metals in solution in the acid filtrate, precipitate or adsorb effectively (97% Cd, 97% Cr, 99% Cu, 82% Ni, 100% Pb and 87% Zn) on the solids of the untreated sludge. Moreover, TCLP tests were done on ashes produced during the incineration of sludge mixed with the acid filtrate produced during sludge decontamination. These tests showed that there were no significant differences, as regards the extractability of metals, between such ashes and those produced during the untreated sludge incineration without addition of filtrate. Therefore, it was predictable that this method can respect the current environmental standards required by the different governmental authorities.

Abstract The approaches to the choice of measures to ensure the environmental safety of closed facilities for the disposal of solid municipal waste (MSW) are considered. Laws of the Russian Federation in terms of requirements for ensuring the safety of waste disposal facilities during the operational and reclamation periods have been studied. Scenarios of the conduct of processes at MSW landfills after reclamation are presented. The article presents the results of engineering and geological research: a comprehensive study of engineering and geological and hydrogeological conditions of the site, composition, condition and properties of soils, the activity of geological processes for making design decisions. Field engineering and geological work, soil sampling from wells have been carried out. Laboratory research of soil samples has been carried out in a soil laboratory. The project of reclamation cover of MSW landfill has been completed, including geosynthetic materials and natural soils, a network of pipelines supplying filtrate for recirculation has been calculated, and a set of work and selection of vegetation at the biological stage of reclamation have been justified. Scenarios of the conduct of processes in the course of reclamation of a waste disposal facility are considered in the case of application of the filtrate recirculation technology with preliminary pH-regulation by changing the structure of the landfill in the first year after reclamation and according to the scheme of the section of the reclaimed landfill upon reaching the stage of destruction of the biodegradable part of the waste. The advantages of the developed reclamation pavement are shown: high cultivation capacity, preservation of drainage properties at high loads, reduced costs for excavation and crushed stone laying, high chemical resistance and environmental friendliness of the material.

In this study, an elemental chlorine free (ECF) bleach plant with a D0(EOP)D1(EP)D2 sequence was studied with the aim of identifying options for significantly decreasing (fresh) water usage in the bleach plant and decreasing the effluent volume. A base-case simulation model for a softwood kraft market pulp mill was made based on a reference model representing the best available techniques as well as data produced in an extensive laboratory pulp bleaching study. This model was used to evaluate increased closure within the bleach plant and the recirculation of bleach plant effluent to the brownstock system and their effects on both the bleach plant and the recovery cycle. The results indicate that it is possible to reduce the fresh water consumption from 15 metric tons/a.d. metric ton in the base case to about 2 metric tons/a.d. metric ton, without increasing the carryover of chemical oxygen demand (COD) to the pulp machine. Nonprocess elements in wood contribute to the levels of metals found in the bleach plant and thus to the risk of precipitates such as calcium oxalate, barium sulfate, and calcium carbonate. The risk of precipitates forming is a key factor determining the possible degree of closure. In addition, chloride concentration in the black liquor is another important factor that is affected by recirculating bleach plant filtrate to the brownstock washer and by the grade of the sodium hydroxide used in the mill.

Successful application of energy efficient dead-end micro-filtration (MF), which does not require recirculation like cross-flow filtration, depends on achieving high recovery rates. In this study, two different types of pilot scale membrane systems (horizontally and vertically stretched membrane filters) were evaluated based on the effects of pre-chlorination, intermittent chlorination and circulation flow by air-scrubbing. Additionally, the effects of operating factors including physical cleaning and chemical cleaning on membrane fouling were examined. The vertically stretched membranes showed better performance than horizontally stretched membranes at filtration fluxes of either 0.55 m/day or 0.78 m/day even under 2.6 to 27.5°C and raw water turbidity higher than 300 units, as long as intermittent chlorination (10 mg/l once a week) along with the circulation flow by air-scrubbing (once in 30 minutes) in the housing were employed. It was demonstrated that the vertically stretched membranes have been operated for one year without chemical cleaning of the membranes, wherein the recovery of raw water as a filtrate was 97.0% or 98.9%.

The bleaching plant of a kraft pulp mill is the sector that consumes water and generates effluent with the highest volume. Water recycling is an attractive option to reduce water consumption and effluent generation. This study evaluated the technical feasibility of using treated effluent as washing water in the bleaching stages. The bleaching sequence was simulated in the laboratory using four types of washing water: deionized water, whitewater, low organic load effluent, and high organic load effluent. To achieve 90% ISO pulp brightness, the ClO2 consumption increased from 8.1 kg ClO2 odt-1 when using water to 13.8 and 16.3 kgClO2 odt-1 for the low and high organic effluents. Physical and optical tests of the hand-sheet papers did not show any statistical difference between various washing waters. The filtrates showed values that did not burden the efficiency of the effluent treatment plant. It was possible to use effluent in the bleaching stages, considering that the filtrates and the produced paper complied with the quality standards.

A recirculating in vitro CAVH system was designed which generated pulsatile blood and filtrate flows. Monitors recorded hydrostatic pressures simultaneously in the arterial, venous and filtrate lines during varying plasma or blood flow rates and predilution (vs postdilution) replacement fluid flow rates. Similar hydrostatic pressure monitoring was carried out during multiple maneuvers to generate suction on the filtrate side of the hemofilter (Amicon® D-20's and Renaflo®‘s). With a plasma flow (Qp) of 100 cc/min and predilution replacement fluid infusion rate of 500 cc/hr, the arterial pressure was 5% greater than during postdilution (p < 0.05). With a blood flow (Qb) of 50 cc/min, predilution fluid replacement rates of 500 and 1000 cc/hr, and vacuum suction applied to the filtrate compartment, the arterial pressure was 33% lower than during postdilution fluid replacement (p < 0.03). Nonetheless, the ultrafiltration rate (UFR) was 10 to 30% higher (p < 0.03). At many other combinations of Qp, Qb and replacement rates and modes, there were no significant changes in arterial pressure. Despite these arterial pressure changes, > 70% of the transmembrane hydrostatic pressure (TMP) was due to the negative pressure induced by filtrate suction (gravity, Gomco®, wall suction, IMED®). The actual pressure in the filtrate compartment measured during Gomco® or wall suction was 3/4 of that stated by their gauges, presumably due to leakage. Maximum wall suction never generated TMP's > 150 mmHg. Using an IMED® 960 as the suction device (bypassing the air alarm), for a Qp of 50, IMED® settings of 300, 600 and 900 cc/hr generated TMP's of 67 ± 3, 77 ± 3, and 97 ± 3 mmHg, respectively. When Qp was 20 cc/min, an IMED® setting of 999 cc/hr generated TMP's consistently < 136 mmHg but UFR was only 668 ± 246 cc/hr. With the IMED® set at 999 cc/hr and Qp of 30 cc/min, the TMP was < 132 mmHg and the UFR was 944 ± 10 cc/hr. No filters ruptured. These suction maneuvers do not generate enough pressure to rupture filters. When Qp is low the IMED® may not generate the UFR one expects. Predilution will probably alleviate this concern.