Water shortage has been an issue for urbanized areas. For the Penang state in Malaysia, it is forecast that there will be a significant increase in water demand in the future. Penang authorities in Malaysia are trying to find an alternative water source to overcome the problem, with one of the options being the Perai River catchment. However, the river water quality was found to be polluted and not suitable to be used for water extraction for domestic consumption. This paper aims to study the pollution level variation due to changes in rainfall during the year in the Perai River Basin, and estimate the TMDL of the river in a particular case for BOD, COD, and NH₃N parameters. A water quality model was developed for the Perai River, Jarak River and Kulim River using InfoWorks ICM. The year 2016 was selected as a model event due to data availability. BOD, COD and NH₃N concentrations were used for TMDL calculation, and the load duration curve approach was used to estimate TMDL. The tidal effect at the downstream of the Perai River was found to impact the data analysis in the river stretch. It was found that pollutant load exceedance was the highest during the rainy season and the problematic pollutant was NH₃N. Thus, local authorities need to focus on tidal and seasonal change factors when developing action plans to manage water quality issues in this basin.

Alluvial aquifer are one of Malaysia’s most abundant groundwater resources, highly demanded in East Coast area. However, the presence of sulfur in these aquifers causes the emission of hydrogen sulfide gas. This research aimed to provide an alternative study for removing sulfur using marble filter media in a cascade column design, where water flows from the highest to the lowest column. Two groups of marble sizes were involved in this filter: pebbles and sand-sized particles. The treatment used raw groundwater with the highest concentration of total sulfur being 537.1 ppm. Sand-sized marble had the highest efficiency of sulfur removal, reaching 98.3% at a flow rate of 0.011 l/s. As a result of the effective filtration, the true color reached 33-34 pt/Co, significantly reduced from the source value of 1000-1012 pt/Co. The application of marble for treating groundwater with the sulfur issue is still novel and promising for groundwater filtration, potentially benefiting consumers facing this problem.

Perai River has been recognized as an additional raw water resource for Penang state. Inadequate waste management can lead to river pollution. River water contamination with metals such as light and heavy metals and metalloid is a global concern that negatively impacts human, plant and aquatic life. Therefore, this paper aims to evaluate the potential sources and impacts of toxic metals at downstream of the Perai River basin. There were 15 sampling points located at possible pollution sources and a sample at the river outfall. In the dry season, samples were taken in two different tidal: low and high tide. According to spatial distribution analysis, Al and Hg levels were observed to be higher than the standard limits during low tide. Meanwhile, Al, As, Hg and Se were significant during high tide. Significant contamination of Al was noticeable upstream during low and even high tide. Pollution of Al and Hg may have started beyond the research zone, as the concentrations were highest upstream during low tide. As was high in certain areas and Se started high at the outfall during high tide. The concentrations gradually decreased to upstream. It concluded that Al, Hg, and As pollution comes from anthropogenic and Se from seawater intrusion. Al and As highest concentrations exceeded the chronic value for aquatic life. Yet, Hg gave a threatening concentration value to plants and aquatic life. Government authorities must take steps to resolve this issue in order to protect the river ecosystem and prevent human health problems.