1. A farmer Mr Maboka is about to install a micro irrigation system on his farm, but needs to decide on the type of filter to use. He hired you as an irrigation specialist. So discuss aspects that you would advise him to take into consideration when selecting a filter type. Moreover, advise him on what would be the best filter for a drip system and why. Finally, he wants to know, the power that would be required to drive a pump, if the pump delivers a flow rate of 640 m3/h at 36 m head at its duty point, at a pump efficiency of 50%. With the cost of running a pump of R5.30 per unit (kWh). Therefore; (a) What would be the power required to drive the pump (calculate)? (b) If the pump was to be run for 7 hours per day for a period of 8 weeks, calculate the electricity costs for 8 weeks.

Water source and quality: The type of water source (well, river, pond, etc.) and its quality (sediment content, chemical composition, etc.) will influence the choice of filter.

Flow rate: The filter should be able to handle the required flow rate of the irrigation system without causing excessive pressure loss.

Filtration level: The filter should be able to remove particles that could clog the drippers or emitters in the micro-irrigation system.

Maintenance: Consider the ease of maintenance, cleaning, and replacement of the filter.

Cost: The filter should be cost-effective, considering both initial investment and long-term maintenance costs.

Best filter for a drip system:

For a drip irrigation system, I would recommend using a disk filter or a screen filter. Disk filters consist of a series of grooved disks stacked together, providing a high filtration level and the ability to handle larger flow rates. Screen filters, on the other hand, use a fine mesh screen to remove particles and are suitable for smaller flow rates. Both types are relatively easy to maintain and clean.

Power required to drive the pump:

To calculate the power required to drive the pump, we can use the following formula:

Power (kW) = (Flow rate (m³/s) × Head (m) × Density of water (kg/m³) × Gravity (m/s²)) / (Pump efficiency × 1000)

Given:

Flow rate: 640 m³/h = 0.178 m³/s

Head: 36 m

Pump efficiency: 50% = 0.5

Density of water: 1000 kg/m³

Gravity: 9.81 m/s²

Power = (0.178 × 36 × 1000 × 9.81) / (0.5 × 1000) = 126.1 kW

Electricity costs for running the pump for 8 weeks:

Running time per day: 7 hours

Number of days in 8 weeks: 8 × 7 = 56 days

Total running time: 7 hours/day × 56 days = 392 hours

Electricity consumption: 126.1 kW × 392 hours = 49,431.2 kWh

Cost per unit: R5.30/kWh

Total electricity cost: 49,431.2 kWh × R5.30/kWh = R262,000 (rounded to the nearest thousand)

In summary, I advise Mr. Maboka to consider a disk filter or a screen filter for his drip irrigation system, taking into account factors such as water quality, flow rate, filtration level, maintenance, and cost. The power required to drive the pump is approximately 126.1 kW. If the pump runs for 7 hours per day for 8 weeks, the total electricity cost would be around R262,000.