{"id":5533,"date":"2021-10-29T08:22:25","date_gmt":"2021-10-29T08:22:25","guid":{"rendered":"https:\/\/www.chemipol.com\/experiencia-en-el-uso-de-chemifloc-pa-47-como-pretratamiento-de-una-osmosis-inversa\/"},"modified":"2026-09-21T12:53:57","modified_gmt":"2026-09-21T12:53:57","slug":"experiencia-en-el-uso-de-chemifloc-pa-47-como-pretratamiento-de-una-osmosis-inversa","status":"publish","type":"post","link":"https:\/\/www.chemipol.com\/en\/experiencia-en-el-uso-de-chemifloc-pa-47-como-pretratamiento-de-una-osmosis-inversa\/","title":{"rendered":"EXPERIENCE OF THE USE OF CHEMIFLOC\u00ae PA 47 AS A REVERSE OSMOSIS PRE-TREATMENT"},"content":{"rendered":"

The Sagra drinking water treatment plant (DWTP)<\/h2><\/div>
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The Sagra East DWTP treats the water that comes from the Almoguera dam to the El Algodor grouping of municipalities at the diversion point of the Noblejas DWTP which crosses the Jarama river in the municipal area of Aranjuez (Madrid).<\/p>\n

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Silt density index (SDI)<\/h2><\/div>
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The SDI, or silt density index, expresses the concentration of colloids in the water, allowing us to categorise the quantity of soiling elements entering RO systems. There is no direct correlation between SDI and turbidity; however, in practical terms, it has been observed that feed waters with a turbidity of less than 1 nephelometric turbidity unit (NTU) or an SDI less than 5, have a low potential for RO membrane fouling. This is an empirical test in which we must keep the pressure and temperature constant over the 15 minutes that it usually lasts. The metering device includes a system whereby water is passed under pressure through a 0.45-micron Millipore membrane (or similar) while the time taken for the passage of a certain amount of water is recorded.<\/p>\n

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When we talk about water treatments, regardless of whether the origin of the water is marine, continental, or treated waste, we cannot ignore the importance of the potential problems caused by the presence of colloidal particles. These are largely responsible for the colour, turbidity, taste, and odour of water. Moreover, their small size (between 10\u22123 and 1 \u03bcm) means that they cannot be naturally filtered out. The origin of colloids is remarkably diverse:<\/p>\n

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  • Microorganisms (bacteria, viruses, and algae).<\/li>\n
  • Minerals (colloidal clays, silts, metal salts, and silica, among other compounds).<\/li>\n
  • Organic (such as surfactants, colourants, and humic or fulvic acids).<\/li>\n<\/ul>\n

    Without proper pre-treatment systems, these small, non-dissolved particles present in feed water will find their way to reverse osmosis (RO) membranes, settling on their surface and thus causing a fouling problem.<\/p>\n

    As a consequence of this fouling (as well as other factors such as age and temperature, etc.), membranes lose their most important characteristics over their normal operating period, especially in terms of the flow rate and the selectivity to salts. Therefore, depending on the membrane operating conditions, there may be a decrease in the flow rate of up to 10\u201312% per year. Thus, the passage of salts through the membrane increases by around 10\u201315% per year. This causes an increase in the feed pressure, a reduction in flow, and a worsening of the quality of the permeate (higher conductivity). Depending on the type of fouling, recovering a contaminated membrane through cleaning is often complex and so it is always better to stop the passage of the causative elements with adequate physical and chemical treatment before feeding the water into the trains.<\/p>\n

    Colloidal particles have a negative electrical charge in natural waters which results in a repulsion phenomenon that prevents them from joining to form larger particles. Therefore, we must neutralise these negative charges by adding positive charges that destabilise them so that the forces of attraction exceed those of repulsion. This leads to agglomeration of the particles\u2014a phenomenon known as coagulation.<\/p>\n

    The chemical reaction of coagulation occurs in three stages:<\/p>\n

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    • Neutralisation of the negative charges of the colloidal particles by adding a coagulant (chemical reagent) with positive ions.<\/li>\n
    • Coagulant reaction and the formation of positively charged colloidal hydrated oxide flocs which attract negatively charged colloidal impurities.<\/li>\n
    • Adsorption (linked bonding or surface bonding) of impurities by the flocs.<\/li>\n<\/ul>\n

      When the reagent is solubilised in water it releases positive ions with a sufficient charge density to attract the colloidal particles and neutralise their charge.<\/p>\n

      The masses formed by the aggregation of destabilised colloidal particles (flocs) have a gelatinous texture and have dimensions in the order of tens to hundreds of microns. These flocs have an appreciable sedimentation rate and can therefore be separated from the water by decantation.<\/p>\n

      The type and amount of coagulant, pH, stirring speed of the mixture, coagulation period, and water temperature are just a few of the many factors that influence the coagulation process.<\/p>\n<\/div>

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      Experience with CHEMIFLOC\u00ae PA 47 at the Sagra drinking water treatment plant<\/strong><\/span><\/h4>\n
      Antecedentes<\/strong><\/span><\/h5>\n

      In 2012, we began to work with the Sagra drinking water treatment plant (DWTP) to search for the most appropriate treatment(s) to reduce high silt density index (SDI) values in water containing high quantities of sulphides.<\/p>\n

      Sulphide ions are reduced forms of sulphur that can appear under anaerobic conditions as the result of the action of sulfate-reducing bacteria. These bacteria (which are usually anaerobic) use sulfate as an energy source, reducing it to sulphur in the process. In the presence of sulphur, iron precipitates and forms Iron(II) sulphide (FeS). This is why ferric chloride is commonly used as a coagulant in these plants.<\/p>\n

      The Sagra facility had a pre-zonation process in place followed by a coagulation chamber in which ferric chloride (FeCl3) was dosed, a flocculation chamber, a lamellar decanter, sand filters, and finally a RO plant.<\/p>\n

      Although FeCl3 has the advantage of forming a large floc that decants immediately, it is also associated with a series of disadvantages such contributing colour to the water, the need for pH adjustment, and most importantly, its efficacy requires very high doses which translates into high plant costs.<\/p>\n

      Since the start of the Sagra plant operation in 2011, and especially during the summer period, the SDI values exceeded 3.2 with peaks of up to 4.<\/p>\n

      At Chemipol we are committed to looking for the best alternative(s) for proper plant functioning and consequently, we also aim to optimise the RO membranes, always within the current regulations cited in Order SAS\/1915\/2009 from 8 July on substances for the treatment of water intended for the production of water for human consumption published by the Spanish Ministry of Health and Social Policy.<\/p>\n<\/div>

      Laboratory jar tests<\/strong><\/span><\/h5>\n

      Based on the information obtained while we studied the situation at the Sagra DWTP before starting the project and considering also that polyacrylamides could not be used in this installation, we identified and preselected a group of coagulants which would be used in the next phase of testing in the laboratory.<\/p>\n<\/div>

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      Chemical coagulation<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div><\/h2><\/div>

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      According to Nelson L. Nemerow, chemical coagulation can be defined as a \u201cunit process to cause the coalescence or aggregation of suspended non-sedimentable material and colloid particles in wastewater\u201d (Nemerow, 1977). This process reduces the forces that repel colloids, forming heavier particles that precipitate through a process known as sedimentation.<\/p>\n<\/div>

      According to Francis Edeline, coagulation is the \u201cchemical process by which a coagulant (regardless of whether it is a chemical or natural substance) is added to water with the aim of destroying the stability of colloids and promoting their aggregation.\u201d<\/p>\n<\/div>

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      Technical specifications<\/p>\n<\/div>\n<\/div>\n<\/div>\n<\/div><\/h2><\/div>

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      CHEMIFLOC\u00ae PA 47 is an organic coagulant based on polyDADMAC (polydiallyldimethylammonium chloride). It is not a dangerous product and is also free of Fe (III) and Al (III) metal ions. It is a liquid with a colourless to yellow appearance.<\/p>\n<\/div>

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      In the laboratory we designed a series of comparative jar tests to simulate the clarification process that occurs in the plant, always keeping in mind that the results do not depend only on the properties of the water to be treated, but also on the construction characteristics of each plant (such as, for example, the shape and dimensions of the decanters or the method used to add coagulants). The jar tests consisted of adding increasing doses of coagulant (measured in parts per million, or ppm) to a series of glass jars containing equal aliquots of the DWTP water. After the appropriate stirring period we then observed the characteristics of the coagulate that had formed, including its physical and chemical properties, floc sizes, and sedimentation time. We also noted the turbidity in each sample after the addition of the coagulant.<\/p>\n<\/div>