Degradation of Toxins and Metabolites of Cyanobacteria and Micropollutants during Biological Sand Filtration

Cyanobacteria produce complex mixtures of secondary metabolites
(cyano-metabolites), some of which are toxic and pose a growing concern
for water utilities. While physical treatments such as filtration
can efficiently remove cells, their lysis can release dissolved cyano-metabolites.
This study investigated the efficiency of laboratory-scale sand filtration
to abate 19 cyano-metabolites representing various structural classes.
Furthermore, abatement of cyano-metabolites in a full-scale sand filtration
is presented. Most cyano-metabolites showed abatement similar to or
higher than the biodegradable benchmark micropollutants atenolol,
paracetamol, and valsartan. Among cyano-metabolites, anabaenopeptins
and cyanopeptolins had the highest abatement, while cyclamides and
microcystin-LR had the lowest abatement. Abiotic controls and formation
trends of 10 identified biotransformation products demonstrated that
biodegradation played a major role in their removal. Laboratory-scale
sand filters showed a sharp increase in biodegradation efficiency
within days due to their adaptation to cyano-metabolites. Increasing
the contact time and temperature both enhanced the abatement of most
compounds, which could be kinetically modeled. High cyano-metabolite
concentrations suppressed their own relative abatement, possibly due
to metabolic enzyme inhibition or saturation. These findings suggest
that sand filtration can serve as a dual-barrier against cyano-metabolites,
including particle removal and biodegradation. However, biodegradation
will be affected by the temperature and cyano-metabolite intake dynamics.

蓝藻（Cyanobacteria）可产生结构复杂的次级代谢产物混合物（蓝藻代谢物，cyano-metabolites），其中部分组分具有毒性，正日益引起供水行业的高度关注。诸如过滤这类物理处理手段虽可高效去除藻细胞，但细胞裂解后会释放溶解性蓝藻代谢物。本研究探究了实验室规模砂滤工艺对19种涵盖不同结构类别的蓝藻代谢物的去除效果，并呈现了全规模砂滤工艺对蓝藻代谢物的去除表现。多数蓝藻代谢物的去除效果优于或等同于作为可生物降解微污染物基准的阿替洛尔（atenolol）、对乙酰氨基酚（paracetamol）与缬沙坦（valsartan）。在各类蓝藻代谢物中，鱼腥藻肽（anabaenopeptins）与蓝藻肽素（cyanopeptolins）的去除率最高，而环酰胺类（cyclamides）与微囊藻毒素-LR（microcystin-LR）的去除率最低。非生物对照实验与10种已鉴定的生物转化产物的生成趋势分析表明，生物降解在蓝藻代谢物的去除过程中发挥了主导作用。实验室规模砂滤柱在适应蓝藻代谢物后，数日内生物降解效率便大幅提升。延长接触时间与升高温度均可增强多数目标化合物的去除效果，该过程可通过动力学模型进行模拟。高浓度蓝藻代谢物会抑制自身的相对去除率，这可能源于代谢酶的抑制作用或酶饱和现象。本研究结果显示，砂滤工艺可作为抵御蓝藻代谢物的双重屏障，兼具颗粒截留与生物降解两种功能。不过，生物降解效果会受到温度与蓝藻代谢物进水负荷动态变化的影响。