Tratamientos avanzados de regeneración de efluentes en la producción de papel

La escasez de agua, un aumento exponencial de la población mundial y una legislación ambiental cada vez más estricta, obliga a establecer restricciones severas respecto al consumo de agua industrial. En este sentido, la industria papelera, caracterizada por un consumo intensivo de agua, es uno de los sectores industriales que más esfuerzo está realizando para reducirlo. Una vez optimizado el uso del agua y los tratamientos de las corrientes internas de proceso, para rentabilizar al máximo el aporte externo de agua de alimentación y reducir a su vez la cantidad de efluente generado, la alternativa más inmediata para alcanzar un mayor cierre de los circuitos es acudir a la regeneración del propio efluente. Sin embargo, con esta medida, el aporte externo de agua de alimentación a la fábrica siempre será necesario, debido a las pérdidas de agua por evaporación, a la disminución de calidad del papel o a problemas en la maquinaria asociados al aumento de contaminación en los circuitos. Otra opción consiste en emplear agua regenerada de origen residual municipal como sustitutivo del agua de alimentación, un recurso de gran atractivo, especialmente en la Comunidad de Madrid. Por tanto, el objetivo general de esta tesis doctoral es minimizar el consumo de agua de alimentación en la fabricación de papel reciclado, estudiando tanto el reciclaje del efluente como el uso de agua regenerada de origen municipal. El estudio de viabilidad de los distintos tratamientos se ha llevado a cabo considerando aspectos ténicos y económicos, dando gran importancia al ahorro energético

Evaluation of MF and UF as pretreatments prior to RO applied to reclaim waste water for fresh water substituion in a paper mill: A practical experience

A pilot plant study has been carried out to compare the effectiveness of different low pressure membrane systems (microfiltration and ultrafiltration) as pretreatments for a reverse osmosis system producing high quality reclaimed water from the effluent of a municipal wastewater treatment plant receiving a high percentage of industrial wastewater. The reclaimed water will be used to substitute fresh water in a paper mill. Although the implemented systems showed several problems derived from the unstable quality of the feed water, they were solid enough to keep a constant permeate quality; i.e. percentages of salt rejection above 99%, efficiencies in the removal of microorganisms to lower values than 1 CFU/100 mL, and final COD results below the detection limit (<5 mg L−1). In short, the quality of the produced reclaimed water was good enough to be used substituting fresh water in a paper mill. An enhanced monitoring of the quality of the water feeding the municipal wastewater treatment plant and an improved corresponding management of the treatments performed in there may be one of the keys to the success of this type of reclamation initiatives. Achieving constant disinfection, an appropriate design of the plants, and a good performance of cleaning operations were very important factors to be considered in order to fight against fouling. Temperature and the soaking time of chemical membrane cleanings were particularly well-optimized for the success of the treatment. Chloramines were compared to free chlorine as disinfection agent achieving satisfactory results

Influence of Water Quality on the Efficiency of Retention Aids Systems for the Paper Industry

It has been reported that about 10-15% of the fresh water intake in a paper mill is used for feeding and diluting retention aids, so significant savings could be achieved by replacing fresh water with process water. Water from different sources and qualitiessfresh water, the outflow from an internal ultrafiltration placed in the machine circuit of a paper mill, and water from a membrane bioreactor used to treat the final effluent of this paper millswere used to prepare a dual retention system consisting of a cationic polyacrylamide and bentonite. While the behavior of bentonite was not significantly affected by the quality of the water used in its preparation, the efficiency of the cationic polyacrylamide was reduced to about 12% when it was prepared with water with high anionic trash content and conductivity as a result of a partial neutralization of the charged groups. The effect of nonionic chemical oxygen demand on the efficiency of the polymer was negligible

Comparison of ultrafiltration and dissolved air flotation efficiencies in industrial units during the papermaking process

The efficiency of an ultrafiltration unit has been studied and compared with a dissolved air flotation system to get water with a suited quality to be reused in the process. The study was done at a paper mill producing light weight coated paper and newsprint paper from 100% recovered paper. Efficiency was analysed by removal of turbidity, cationic demand, total and dissolved chemical oxygen demand, hardness, sulphates and microstickies. Moreover, the performance of the ultrafiltration unit and the membranes were studied deeply, analysing its variability during the filtration process. As expected, the ultrafiltration gave higher removal efficiencies than the dissolved air flotation cell in parameters like turbidity, cationic demand, dissolved chemical oxygen demand and microstickies. The greatest difference in performance between the units concerned cationic demand and dissolved chemical oxygen demand. Ultrafiltration was influenced by the operating time, decreasing the removal efficiency of the dissolved fraction by 75% and of the colloidal fraction by 30% after 312 of running. Membrane autopsy, carried out to identify the cause of poor membrane performance, showed that the active layer was degraded due to the effect of suspended solids

pH and particle structure effects on silica removal by coagulation

Producción CientíficaCoagulation is presented as an efficient alternative to reduce the silica content in effluents from recovered-paper mills that are intended to be recycled by a final reverse-osmosis (RO) step. Coagulation pretreatment by several polyaluminum chlorides (PACls) or FeCl3 was optimized prior to the RO process. PACls with low alumina content and high basicity achieved almost a 100 % removal of silica at pH 10.5. A good reduction of the silica content was attained without regulating the pH by adding one of these PACls. Silica removal was related to the structure of the produced clots in which cylindrical particles produced higher silica removal. All coagulants removed more than 50 % of the chemical oxygen demand (COD).Comunidad Autónoma de Madrid - (Proyecto P2009/AMB-1480)Ministerio de Ciencia e Innovación - (Proyecto CTM2008-06886-C02- 01)Comisión Europea - (Proyecto 211534

Application of multi-barrier membrane filtration technologies to reclaim municipal wastewater for industrial use

Producción CientíficaThe significant percentage of the world water consumption devoted to industrial use, along with an increasingly higher environmental concern of society, has awaken the interest of industry on using municipal reclaimed water for replacing fresh water use coming from utilities or natural resources. Depending on the type of industry and the specific application, water must meet certain quality requirements. Therefore, those water quality standards that are required for those most relevant industrial applications wherein the use of reclaimed water has noticeably been reported are herewith reviewed. Although the use of internal water treatments for recycling and reusing their own effluents has recently and widely been reported within many industrial sectors worldwide, the substitution of fresh water by reclaimed municipal wastewater has yet to be extended much. The increasing proportion of municipal wastewater reclamation plants that rely on membrane filtration technologies versus the total number of reclamation facilities that are distributed worldwide is also assessed within this review, including the discussion of their main related drawbacks.Comunidad Autónoma de Madrid - (Proyecto S-0505/AMB-0100)Ministerio de Ciencia e Innovación - (Proyecto CTM2008-06886-C02- 01)Unión Europea - (Project 211534

Combining coagulation, softening and flocculation to dispose reverse osmosis retentates

The concentrated stream of a reverse osmosis unit was treated by coagulation, softening and flocculation to reduce conductivity and refractory organic matter content. Different polyaluminium chlorides and one ferric salt were used as coagulants, lime was added as softener, and two polymers (anionic and cationic polyacrylamides) were tested as flocculants. Coagulants reduced significantly the presence of refractory compounds by themselves, although conductivity increased. Lime addition decreased conductivity forming precipitates of CaCO3 and Mg(OH)2. When coagulation was combined with flocculation without adding lime, the anionic flocculant was more effective than the cationic one because the specific high hardness of water supplied enough Ca2+ and Mg2+ to promote the formation of bigger flocs, bridging the slightly negative coagula and anionic groups of the polymer; although they also reduced the efficiency of the cationic polyacrylamide. None of the tested flocculants showed any effect on conductivity and refractory organic matter reduction when lime was added

Optimization of conventional Fenton and ultraviolet-assisted oxidation processes for the treatment of reverse osmosis retentate from a paper mill

According to current environmental legislation concerned with water scarcity, paper industry is being forced to adopt a zero liquid effluent policy. In consequence, reverse osmosis (RO) systems are being assessed as the final step of effluent treatment trains aiming to recover final wastewater and reuse it as process water. One of the most important drawbacks of these treatments is the production of a retentated stream, which is usually highly loaded with biorecalcitrant organic matter and inorganics; and this effluent must meet current legislation stringent constraints before being ultimately disposed. The treatment of biorefractory RO retentate from a paper mill by several promising advanced oxidation processes (AOPs) – conventional Fenton, photo-Fenton and photocatalysis – was optimized considering the effect and interaction of reaction parameters; particularly using response surface methodology (RSM) when appropriate (Fenton processes). The economical cost of these treatments was also comparatively assessed. Photo-Fenton process was able to totally remove the COD of the retentate, and resulted even operatively cheaper at high COD removal levels than conventional Fenton, which achieved an 80% reduction of the COD at best. In addition, although these optimal results were produced at pH = 2.8, it was also tested that Fenton processes are able to achieve good COD reduction efficiencies (>60%) without adjusting the initial pH value, provided the natural pH of this wastewater was close to neutral. Finally, although TiO2-photocatalysis showed the least efficient and most expensive figures, it improved the biodegradability of the retentate, so its combination with a final biological step almost achieved the total removal of the COD

Replacement of fresh water use by final effluent recovery in a highly optimized 100% recovered paper mill

A further closure of the water circuit in paper mills with a relative high optimization of their water network is limited by the increase of contamination in the water and runnability problems of the paper machine. Therefore, new strategies for saving water must be focussed on the treatment of final effluents of the paper mill, aiming to obtain high quality water that may replace fresh water use in some applications. An appropriate treatment train performed at pilot scale,consisting on a previous clarification stage followed by anaerobic and aerobic treatments,ultrafiltration, and reverse osmosis, made possible producing the highest water quality from the final effluent of the mill. Anaerobic pre-treatment showed very good performance assisting the aerobic stage on removing organics and sulphates, besides it produced enough biogas for being considered as cost-effective. Permeate recovery depended on the silica content of the paper mill effluent, and it was limited to a 50–60%. The reject of the membranes fully met the legislation requirements imposed to effluents arriving to municipal wastewater treatment plants