This study was aimed at harvesting of microalgae, Chlorella pyrenoidosa, by using Bottom ash (BA). Utilization of an inexpensive and an easily available BA as a flocculant can be the alternative solution for reducing the harvesting cost of the microalgae and on the other side best way to utilize the unused waste from coal based thermal power plants. Herein, aimed flocculation process was evaluated and optimized through the statistical method, response surface methodology (RSM) with Box Behnken Design (BBD). Optimized conditions for harvesting were found to be best with BA concentration of 100 mgL⁻¹, temperature (50 ºC), pH (6.5), and incubation time (60 min) for achieving a maximum yield of 97.9%. The results obtained indicated that BA is a promising flocculant that requires low dose, temperature, and time for a high coagulation and agglomeration of the microalgae. BA is a cost effective and an environmentally friendly flocculant that could neutralize the Zeta potential ($\zeta$) of surface charge of the microalgal cell surface. The morphological changes of microalgae were also analyzed on various temperatures with scanning electron microscopy (SEM), and elemental composition on surface by energy dispersive X-ray spectroscopy (EDS) images with and without flocculant.

这项研究旨在通过使用底灰（BA）收获微藻，小球藻（Chlorella pyrenoidosa）。使用廉价且易于获得的BA作为絮凝剂可以作为降低微藻类收获成本的替代解决方案，并且是利用燃煤热电厂未使用废物的最佳方法。在此，采用Box Behnken Design（BBD）通过统计方法，响应面方法（RSM）对目标絮凝过程进行了评估和优化。发现最佳收获条件是BA浓度为100 mgL ^-1时最佳，温度（50ºC），pH（6.5）和孵育时间（60分钟）以达到97.9％的最大产率。获得的结果表明，BA是一种有前途的絮凝剂，需要低剂量，低温度和低时间才能使微藻类高度凝结。BA是一种具有成本效益的环保絮凝剂，可以抵消Zeta的潜力（$\zeta$）微藻细胞表面的表面电荷。还通过扫描电子显微镜（SEM）在各种温度下分析了微藻的形态变化，并通过有和没有絮凝剂的能量色散X射线光谱（EDS）图像分析了表面的元素组成。