Compact Drinking Water Unit - 15 m³/h

Description

The compact drinking water unit is a containerised unit, ready for use, assembled and fully tested in our workshop.

The unit is producing 15 m³/h drinking water from surface water.

Outside dimensions: 6058 mm x 2438 mm x H 2895 mm (in shipping container 20 ft)

Empty weight: +/- 5 tons

Power supply: 7 kW for the unit with the raw water pump

Raw water:

Raw water is surface water, without sand, with the following maximum concentrations:

• Suspended solids: 2000 mg/l
• Iron: 15 mg/l
• Manganese:  5 mg/l
• total:  50-5000 col/100ml (MPN)

Other parameters (like, as an example, nitrate, heavy metals, micro-pollutants…) which are not removed should respect the maximum limits according to WHO recommendations for drinking water.

Treated water:

Treated water quality fulfil the WHO recommendations. Turbidity is lower than 1 NTU. pH is higher than 7 and lower than 8.

Advantages

The proposed system basically includes a raw water pump, installed on a floater, feeding two-step treatment: flocculation-decantation, followed by a multilayer filtration. It also includes a pH correction treatment to reduce water aggressiveness and a disinfection.

Compared media filtration or membrane filtration-based systems, it allows production of drinking water from surface water with fluctuations in suspended solids concentrations. During heavy rain periods, water quality varies, and it becomes heavily loaded with suspended solids, causing rapid clogging of the filtration only based systems. When a decantation is provided upstream of filtration, it is possible to remove a large part of suspended solids before water reaches the filtration unit.

Operation

Raw water flows through a Y-filter for safety screening. A spare unit is provided. Then, chemicals are dosed:

• Calcium hypochlorite for pre-chlorination,
• Aluminium sulphate for coagulation,
• Sodium carbonate to adjust flocculation pH (dosage of lime slurry is optional).

Water, enriched with the reagents, flows through a static mixer which ensures their dispersion. An ejector allows sludge recirculation to facilitate flocculation. Water then enters the flocculation area of the settling tank. To limit the electro-mechanical equipment, the flocculation energy is generated by hydraulic head losses in a perforated pipe and a baffle.

Flocculated water enters the settler under the tubular packing, made of PVC corrugated plates, assembled back to back and forming a honeycomb structure. Packing is set with a 60° slope, allowing sludge to slide downwards along the plates and reach a prismatic sludge pocket under the flocculation and settling zones.

Sludge drainage is done manually.

Settled water is collected on the upper side, through to two perforated pipes, and flows to a storage tank located on the side.

Settled water is pumped through two identical multilayer (anthracite-fine sand-gravel) pressure filters. Filters operate in parallel during production run and are equipped with piping and valves allowing backwash. All valves are manually operated.

The following reagents are dosed into the filtered water:

• Calcium hypochlorite for disinfection,
• Sodium carbonate to increase pH and limit water aggressiveness and corrosivity (dosage of lime slurry upstream of filtration is optional)

The filtered water must be stored in a treated water storage tank (option) achieving a 30 minutes contact time as a minimum, ensuring good disinfection. Minimum capacity of tank is 8 m³.

Reagents preparation is done in a set of three dosing tanks.

They are injected using 5 membrane metering pumps with manually-set stroke length. 

Filters Backwash

Filter backwash is done manually.

Filtered water on filter A is used to backwash filter B, and vice versa.

The first filtrate is cleared out.

An extra connection is provided to backwash filter with treated water when needed.

Options

• Centrifugal sand separator,
• Treated water tank,
• Batteries to accumulate electrical energy not consumed by the unit,
• Security and lighting of the site,
• On site delivery (base: one container pre-assembled in our workshop or as an option, equipment installed on several skids to be locally assembled),
• Technical assistance with several follow-up missions (Commissioning and start-up included in basic delivery),
• Lime instead of sodium carbonate,
• Delivery of chemicals (reagents for start-up included in basic delivery).

Reagents consumption

Consumption are calculated based on average surface water quality (temperature: 27°C - pH: 6.5 – m-Alk: 25 ppm CaCO3 – Aluminium sulphate dosage: 30 mg/l).

Based on 5 m³/h treated water production during 8 hours per day, the monthly consumption of chemicals is estimated as follows:

• Calcium hypochlorite - powder (70% active chlorine): 35 kg
• Aluminium sulphate - powder: 115 kg
• Anhydrous sodium carbonate (dense): 160 kg

Plant can be adapted to use lime as an option. In this case, monthly consumption is 70 kg.

Miscellaneous

Delivery also includes:

• Raw water pump 16 m³/h-30m installed on a floater, including DN 65 flexible hose,
• Seaworthy packing,
• Commissioning and start up,
• Delivery of chemicals for start-up (+/- 3 months),
• Spare parts for 2 years operations (for normal use of equipment), set of tools, grease,
• Lab instruments:
  • 1 turbidity-meter,
  • 1 comparator for free chlorine testing,
  • 1 field pH-meter,
  • 2 aerometers for the control of reagents concentration

Water cost

Considering a daily use of 20 hours for 15m³/h, costs are as follows:

Reagents                          31,66  EUR/day

Electricity (network)     20,32  EUR/day

Personnel                           9,09  EUR/day

Wear parts                          0,51  EUR/m³

Water cost                       0,22  EUR/m³