Buổi 92: Reading – Bài đọc dài nhiều dạng (khử mặn nước biển), tính giờ 20 phút

Turning the sea into drinking water

(Bài đọc tự viết; thành phố, nhà máy, nhân vật và số liệu là giả định.)

A For coastal cities facing water shortages, the ocean offers an apparently unlimited supply – if only the salt can be removed. Desalination, the process of turning seawater into freshwater, has existed for decades, but improvements in technology have made it an increasingly common option for regions where rivers and groundwater can no longer meet demand.

B Most modern plants use a method called reverse osmosis. Seawater is first filtered to remove sand and larger particles. It is then pushed at very high pressure through special membranes with extremely small holes, which allow water molecules to pass through but hold back the salt. The freshwater that emerges is treated with minerals to improve its taste before entering the supply network.

C The main drawback is energy. Forcing water through membranes requires a great deal of power, which makes desalinated water considerably more expensive than water from conventional sources. Where the electricity comes from fossil fuels, the process can also add significantly to carbon emissions. Some newer plants have attempted to address this by using solar or wind power, and by recovering energy from the high-pressure water as it leaves the membranes.

D A second concern is brine – the highly salty liquid left over after freshwater has been extracted. If it is discharged directly into the sea near the coast, it can sink to the seabed and harm marine life. Engineers at the hypothetical Port Ellis plant reduced this risk by releasing the brine through long pipes with many small outlets, so that it mixes more quickly with surrounding seawater. Even so, environmental groups argue that the long-term effects are not yet fully understood.

E Not everyone believes desalination is the right answer. Hydrologist Dr Samuel Okafor points out that many cities lose large amounts of water through leaking pipes. “Before building an expensive plant, a city should ask whether it can save the same amount of water by fixing its existing network,” he says. He acknowledges, however, that for some very dry regions, desalination may be the only realistic way to secure a reliable supply.

F For now, desalination seems likely to play a growing but limited role. It is most viable for wealthy coastal cities with few alternatives. Elsewhere, reducing waste, reusing treated wastewater and managing demand are generally cheaper first steps.

Incident report #0412 (văn bản giả định)

Date: 2 March · Location: Warehouse B, loading bay 3 What happened: Water leaked through the roof during heavy rain, wetting 14 boxes of packaging. Immediate action: Boxes moved to dry area; buckets placed under leak. Root cause: Blocked gutter above bay 3. Corrective action: Gutter cleared on 3 March. All gutters to be checked every three months. Follow-up: Facilities manager to confirm roof inspection by 31 March.