**2.1 Seeds**

*Moringa oleifera* seeds which are not harmful to human and do not have significant drawbacks have been applied for wastewater treatment [4–6]. The seeds showed natural coagulation activity which is similar and even better than aluminium sulphate (alum) [27, 28].

The seed oil is extracted by different methods either by solvent (cake residue) or by mechanical press (press cake). Both seed extracts were used in heavy metal removal.

Cake residue preparation: method (a): the seed husks are removed manually, the kernel is ground, and the kernel powder is then mixed with ethanol and mixed using a magnetic stirrer for 30 min. The mixture is then centrifuged at 4000 rpm for 10 min. The residual solid (seed cake) was dried at room temperature for 24 h [3]. The stock preparation was prepared with different concentrations: 10,000,

20,000, and 30,000 mg/L. The different concentrations were applied to wastewater, and jar test was performed with an initial speed of 150 rpm for 2 min, reduced to 50 rpm for 25 min, and then left to settle for 1 h [29].

Method (b): oil was extracted by Soxhlet extraction method [29]. Extraction thimble is filled with 10 g of *Moringa oleifera* seed powder. Hexane solvent (170 mL) was poured into a round bottom flask. The heater is turned on until the solvent is boiling; the oil was extracted within around 45 min. *Moringa oleifera* cake residue was collected from the thimble and dried in an oven at 50°C overnight. Once the oil was fully removed from the *Moringa oleifera* seed, the seed cake residue could be used in water treatment [30]. The oil was extracted from the seeds because the presence of oil in the *Moringa oleifera* seed would affect the coagulation activity and heavy metal removal [19]. The higher the oil content in *Moringa oleifera* seed, the lower the performance of the *Moringa oleifera* cake residue in water treatment process.

Press cake preparation: the seeds were pressed mechanically by Mitomasa Sdn. Bhd., Kuala Lumpur, Malaysia, and the press cake was bought from the company and applied in water treatment [31]. Press cake was soaked with water overnight to get the remaining oil. And the clean press cake was used in this experimental work. The moisture content was calculated to get the right mass for the biosorbent added to water [31]. The synthetic turbid water was used for biosorption test on Cu(II) removal from water by *Moringa oleifera* press cake.

## **2.2 Leaves**

*Moringa oleifera* leaves were collected from a nearby area at Universiti Malaysia Pahang, Kuantan, Pahang, Malaysia, dried and ground, and sieved using a sieve shaker to 2, 1 mm, 500, 250, and < 250 μm.

*Moringa oleifera* leaf extract was used in aqueous solutions as a good sorbent for Pb(II) [32]. It was used for optimization of Cd(II), Cu(II), and Ni(II) biosorption [33] and removing of Cd(II) from wastewater [34].
