Corsino Santo Fabio, Di Bella Gaetano, Traina Francesco, Montes Lucia Argiz, Val Del Rio Angeles, Corral Anuska Mosquera, Torregrossa Michele, Viviani Gaspare
Department of Engineering, Università di Palermo, 90128 Palermo, Italy.
Faculty of Engineering and Architecture, Università di Enna, 94100 Enna, Italy.
Membranes (Basel). 2022 Jul 12;12(7):703. doi: 10.3390/membranes12070703.
Fouling is considered one of the main drawbacks of membrane bioreactor (MBR) technology. Among the main fouling agents, extracellular polymeric substances (EPS) are considered one of the most impactful since they cause the decrease of sludge filterability and decline of membrane flux in the long term. The present study investigated a biological strategy to reduce the membrane-fouling tendency in MBR systems. This consisted of seeding the reactor with activated sludge enriched in microorganisms with polyhydroxyalkanoate (PHA) storage ability and by imposing proper operating conditions to drive the carbon toward intracellular (PHA) rather than extracellular (EPS) accumulation. For that purpose, an MBR lab-scale plant was operated for 175 days, divided into four periods (1-4) according to different food to microorganisms' ratios (F/M) (0.80 kg COD kg TSS d (Period 1), 0.13 kg COD kg TSS d (Period 2), 0.28 kg COD kg TSS d (Period 3), and 0.38 kg COD kg TSS d (Period 4)). The application of the feast/famine strategy favored the accumulation of intracellular polymers by bacteria. The increase of the PHA accumulation inside the cells corresponded to the decrease of EPS and an F/M of 0.40-0.50 kg COD kg TSS d was found as optimum to maximize the PHA production, while minimizing EPS. The lowest EPS content in the sludge (18% of total suspended solids) that corresponded to the maximum content of PHA (9.3%) was found in Period 4 and determined significant mitigation of the fouling rate, whose value was close to 0.10 × 10 m h. Thus, by imposing proper operating conditions, it was possible to drive the organic matter toward PHA accumulation. Moreover, a lower EPS content corresponded to a decrease in the irreversible fouling mechanism, which would imply a lower frequency of the extraordinary cleaning operations. This study highlighted the possibility of obtaining a double benefit by applying an MBR system in the frame of wastewater valorization: minimizing the fouling tendency of the membrane and recovery precursors of bioplastics from wastewater in line with the circular economy model.
膜污染被认为是膜生物反应器（MBR）技术的主要缺点之一。在主要的污染因子中，胞外聚合物（EPS）被认为是影响最大的因素之一，因为从长远来看，它们会导致污泥过滤性下降和膜通量降低。本研究调查了一种降低MBR系统中膜污染倾向的生物学策略。该策略包括向反应器中接种富含具有聚羟基脂肪酸酯（PHA）储存能力的微生物的活性污泥，并施加适当的操作条件，以使碳向细胞内（PHA）而非细胞外（EPS）积累。为此，一个MBR实验室规模的装置运行了175天，根据不同的食物与微生物比（F/M）分为四个阶段（1-4）（第1阶段为0.80 kg COD/kg TSS·d，第2阶段为0.13 kg COD/kg TSS·d，第3阶段为0.28 kg COD/kg TSS·d，第4阶段为0.38 kg COD/kg TSS·d）。 feast/famine策略的应用有利于细菌积累细胞内聚合物。细胞内PHA积累的增加对应着EPS的减少，发现F/M为0.40-0.50 kg COD/kg TSS·d是使PHA产量最大化同时使EPS最小化的最佳值。在第4阶段发现污泥中最低的EPS含量（占总悬浮固体的18%）对应着最高的PHA含量（9.3%），并确定污垢率显著降低，其值接近0.10×10 m/h。因此，通过施加适当的操作条件，可以使有机物向PHA积累。此外，较低的EPS含量对应着不可逆污染机制的减少，这意味着非常规清洗操作的频率较低。本研究强调了在废水增值框架内应用MBR系统获得双重效益的可能性：最小化膜的污染倾向，并根据循环经济模式从废水中回收生物塑料的前体。
