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http://www.itn-nanovation.com/applications/case-studies/ground-water-retrofit-of-gravity-sand-filters.html

Ground Water Retrofit of Gravity Sand Filters

Common ground water treatment plants with high iron concentrations are typically designed with pre-treatment steps including a softener system and sand filters. The main challenge for the operator is to find the the suitable process operation with low operational expenses, using less chemicals, producing maximum quality of filtered water  for a stable RO process and minimal loss of water. In September 2012, ItN Nanovation started a plant tuning program for an existing ground water treatment plant in Riyadh, Saudi Arabia. An implementation of CFM Systems®  using existing gravity sand filter civil works structure was proposed. A successfully finalized piloting has shown that CFM implementation enables a plant expansion increasing capacities by more than 100% and a recovery rate of 99.6 % at very low operational expenses.

Client    

    • NWC National Water Company, Riyadh Saudi Arabia

    Project Status    

    • September 2012 - January 2013 Piloting at site for performance study and CAPEX & OPEX study
    • February 2013 Submittal of retrofit concept (currently under evaluation by client)

    Project Targets    

      • Removal of Iron and micro organism
      • Improvement of filtered water quality
      • Improvement of recovery rate
      • Expansion of plant capacity by using existing sand filter civil works structure only

      Capacity    

      • 20,400 m³/d (for one retrofitted sand filter)
      • 122,400 m³/d (for all retrofitted sand filters)

      Parameter

      Unit

      Raw Water

      Softener & Sand Filter
      (as designed)

      Sand Filter without Softener
      (as currently operated)

      CFM Systems®
      (based on piloting results)

      Capacity

      %

      100

      70

      212

      Iron

      ppm

      1.3

      < 0.02

      0.04–0.15

      0.011 (avg)

      Total Bacterial Counts

      CFU/ml

      Over account

      NA

      NA

      20 (NSF test average Log-Removal at 4.3)

      Turbidity

      NTU

      3.1–7.1

      < 0.20

      0.2–0.4

      0.12 (avg)

      SDI

      < 2

      2–4

      0.37 (avg)

      Recovery Rate

      %

      96 (including backwash waste recovery system)

      94 (including backwash waste recovery system)

      99.6 (without backwash waste recovery system)

      Power Consumption

      kWhr/m³

      0.040

      0.060

      0.106

      USD/m³

      0.0030

      0.0040

      0.0073

      Complete Pre-Treatment Chemical Consumption

      USD/m³

      0.0840

      0.0020

      0.0125 (includes CFM CIP chemical cleaning)

      Total considered OPEX

      USD/m³

      0.0870

      0.0060

      0.0198

      %

      100.0

      6.9

      22.8

      RO Operation

      Due to efficient pre-treatment and excellent RO feed stable operation as designed

      Limited removal of Fe leads to increased risks for fouling and frequent chemical cleaning requirements

      Retrofitted pre-treatment leads to excellent RO feed quality and stable operation with minimum cleaning requirements

      The existing plant design enables an operation of pre-treatment steps with and without softener system. Due to very high softener consumptions, the client has already eliminated the softener step, which led to tremendous OPEX savings.

      On the other hand, the complete Fe concentration needs to be directly filtered through the sand filters without pre-removal as a result of the missing softener step . A reduced hydraulic flow and more frequent and longer backwash requirements led to a significantly reduced plant capacity as well as reduced recovery rates.

      In addition, the filtered water quality of sand filters operating without softener system is not satisfying. During Fe peak concentrations the filtered water characteristics exceed RO feed specifications leading to Fe fouling and thus frequent chemical cleaning.

      Particularly the reduced plant capacity and increased water losses were the main reasons for the client to investigate new technologies.

      During a piloting period of 6 months ItN Nanovation has proven the outstanding performance of CFM Systems® to the lient. The quality of filtered water was raised to excellent levels; the recovery rate has been maximized.

      ItN Nanovation has additionally designed a retrofit option using the existing sand filter civil works structure for implementation of CFM Systems®. The retrofit design leads to a maximum plant capacity option. The existing two basins design with gravity sand filter and a capacity of 400 m/hr can be increased to up to 850 m³/hr by implementation of CFM Systems®.

      Existing design with required civil works modifications only

      Complete CFM process integration with Filtration Racks