중동 국가들은 증가하는 인구를 위해 충분한 식수와 농업용수를 확보해야하는 어려움에 직면해 있다. 

바레인(Bahrain)에서는 국내 최대 규모의 하수 처리장이 대대적인 재단장을 거쳤고, 슐처(Sulzer)의 자회사인 노르딕 워터(Nordic Water)는 처리장의 기존 모래 필터를 ‘DynaSand 필터’로 교체했다. 

이는 최근 여과 시스템의 확장과 함께 처리장이 관개를 위해 매일 올림픽 수영장 100개 규모에 해당하는 하수 25만㎥를 처리할 수 있게 했다. 

하수 처리장은 지역의 동식물과 주민을 보호하기 위해 환경으로 재배출되는 모든 물에 대한 엄격한 품질 기준을 충족해야 한다.

그러나, 일일 처리 용량이 증가함에 따라 설비에 대한 부담이 증가하고 있으며, 이 때문에 현장의 설치 공간을 늘리지 않고, 장비를 업그레이드 및 확장해야 하는 경우가 많다.

바레인에서는 농업용수에 대한 수요 증가로 인해 국내 최대 규모 수처리 시설을 대규모로 재단장 했다. 특히 부유물질, 생물학적 물질, 미세플라스틱 및 인을 제거하기 위해 설계된 원래의 모래 필터의 교체가 필요했다. 

이 초기 프로젝트를 위해 효율성과 처리량을 크게 향상시킨 혁신적인 솔루션을 가진 노르딕 워터(Nordic Water)가 협력했다.

필터의 기존 설치 공간을 유지해야 했기 때문에 이 프로젝트는 원래 있던 장비의 내부를 제거하고 기존 20개의 콘크리트 수조에 160개의 DynaSand 필터를 설치했다. 기존 시스템과 비교했을 때, 새로운 모래 필터는 역세척 없이 지속적으로 작동할 수 있는 기능 등 여러 가지 이점을 제공했다.

DynaSand 필터는 원수를 필터의 바닥으로 보내고, 물이 여과지 베드(media bed)를 통해 위로 흘러 올라갈 때 고형물이 제거된다. 여과액의 일부는 폐 고형물의 세척 및 이동에 사용된다. 동시에 에어 리프트 펌프(air lift pump)는 필터 바닥에서 세척 상자와 모래 세척기로 매체를 끌어 올려 이물질을 분리하고 배출한다.

이러한 성공을 거둔 노르딕 워터는 2024년 1분기에 완료될 예정인 확장 프로젝트에 다시 참여하게 됐다. 기본적으로, 처리해야 할 일일 물의 양은 마지막 프로젝트 이후 두 배로 증가했으며 가능한 한 가장 작은 설치 공간 내에서 이러한 증가를 처리하는 데 필요한 여과 장비가 요구됐다.

이러한 요구 사항을 고려할 때 특수 목적의 콘크리트 수조가 최고의 솔루션이었다. 작은 외곽선 안에 넓은 표면적을 제공하는 추가적인 160개의 필터는 처리장에서 매일 25만㎥의 하수를 재활용할 수 있게 했다. 

모래 여과 외에도 지역 주민들에게 심각한 위험을 초래하는 기생충 알 문제를 해결해야 했다.

한편, 세계보건기구(WHO)는 하수에 기생충 알이 존재한다는 점을 강조했으며 이러한 병원체를 재이용수과 관련된 가장 큰 건강 위험으로 간주했다. WHO는 필수 표준으로 1 helminth egg/L 미만을 권장하며, 노르딕 워터 솔루션은 이 기준을 능가했다.

[원문보기]

Recycling water for agriculture in Bahrain
DynaSand filters enable rejuvenation of wastewater treatment plant and supply of irrigation water

Countries in the Middle East face a constant challenge with delivering sufficient water for an increasing population, both for drinking water and irrigation for agriculture. In Bahrain, the largest water treatment works in the country has undergone a huge redevelopment and Nordic Water, a Sulzer brand, has retrofitted the original sand filter basins with DynaSand filters. This, together with a recent expansion of the filtration systems, has enabled the plant to treat 250’000 m3/day for irrigation, the equivalent of 100 Olympic swimming pools every day.

Wastewater treatment plants must meet stringent quality standards for all water discharged back to the environment. This is to protect local flora and fauna as well as the local population. However, as the daily volumes increase, facilities are put under increasing pressure, which means the equipment needs to be upgraded and expanded - often without increasing the footprint of the site.

Repurposing filter basins

In Bahrain, the demand for greater volumes of water for agriculture led to the large-scale refurbishment of one of the largest treatment works in the country. The original sand filters, designed to remove suspended solids, biological materials, microplastics as well as phosphorus, needed replacement. This initial project was contracted to Nordic Water, which had an innovative solution that has significantly increased efficiency and throughput.

With a need to retain the existing footprint of the filters, the project removed the internals of the original equipment and installed 160 DynaSand filters in the original 20 concrete basins. Compared to the legacy system, the new sand filters delivered several advantages, not least the ability to operate continuously without back-washing.

DynaSand filters direct the raw water to the base of the filter and the solids are removed as the water flows up through the media bed. A small part of the filtrate is used for cleaning and the transfer of waste solids. At the same time, an air lift pump draws the media from the bottom of the filter up to the wash box and into the sand washer, where the debris is separated and discharged.

Expanding on success

Having achieved such success, Nordic Water was re-engaged for the expansion project, which is due for completion in the first quarter of 2024. Essentially, the daily volume of water to be treated has doubled since the last project and the filtration equipment needed to handle this increase within the smallest possible footprint.

Considering these requirements, the purpose-built concrete basins were the best solution. Providing a large filter surface area within a small outline, the additional 160 filters have enabled 250’000 m3 of wastewater to be recycled every day by the treatment plant. This simple, but very effective solution has been delivered as part of a coordinated expansion of the original site.

In addition to the sand filtration, there was also a need to tackle a problem with helminth eggs, which pose a significant risk to the local population. The World Health Organization (WHO) has placed a large emphasis on the presence of helminth eggs in wastewater and has deemed these pathogens as the greatest microbiological health risk associated with its reuse. It recommends less than 1 helminth egg / liter as the required standard, which has been surpassed by Nordic Water’s solution.

High-quality solutions

At the time of this WHO report, 1989, the recommended treatment was retention of wastewater in stabilization ponds for 8-10 days. This would clearly create a bottleneck in the process and require a large land area, both of which needed to be avoided in this project.

Nordic Water has addressed this challenge with the addition of nine DynaDisc filters to be used as a pre-filter for the new DynaSand installation. This would remove the helminths, such as hookworm larvae and Ascaris lumbricoides eggs, which pose a particular risk to farm workers who are in contact with wastewater used for irrigation purposes.

Today, the volume of water, equivalent to 100 Olympic-sized swimming pools, that was previously being discharged into the sea every day is being recycled by the treatment plant at such high quality levels that it can all be used for irrigation. The new filtration process is also considerably less expensive to operate than the legacy system. As a result of this large-scale project, the surrounding land has been transformed over the past 13 years and this is set to continue with the most recent facility expansion.

[출처 = Sulzer(https://www.sulzer.com/en/shared/case-studies/recycling-water-for-agriculture-in-bahrain) / 2023년 12월 11일]

[번역 = 박원희 기자]