Microbial Contamination and Die-Off on Crops Irrigated With Reclaimed Wastewater

Wastewater treatment plants significantly reduce the microbe levels in water. However, the remaining microbes may regrow in the nutrient-rich wastewater effluent.
Therefore, using this reclaimed effluent as a secondary water source can potentially contaminate crops. For this study, an agricultural field was irrigated using reclaimed wastewater from the Hyrum Wastewater Treatment Plant. The water was tested before and after irrigation to determine the microbial load applied to the crops. Then, daily plant samples were collected to determine both the initial microbial contamination level and the die-off after the irrigation event. All samples were tested on IDEXX’s Colilert and Enterolert trays. These trays contain large and small wells that each give positive/negative results. The different sized wells act like different dilutions to help quantify bacteria concentrations. Positive wells are counted and an IDEXX table used to convert the well counts into MPN counts for coliforms, E. coli, and Enterococcus, all found in high levels in wastewater influent. Test results demonstrated microbial regrowth in the reclaimed wastewater system. Additionally, the reclaimed water contaminated the irrigated plants and the contamination level was reduced significantly in the first 48 hours after wastewater application.

污水处理厂显著降低了水中的微生物水平。然而，剩余的微生物可能在富含营养的废水排放中重新生长。因此，将这种再生废水作为二级水源可能会潜在地污染作物。在本研究中，一块农田使用来自Hyrum污水处理厂的再生废水进行灌溉。灌溉前后对水质进行了检测，以确定施加于作物上的微生物负荷。随后，每日收集植物样本，以确定灌溉事件后的初始微生物污染水平和微生物死亡情况。所有样本均在IDEXX公司的Colilert和Enterolert板上进行检测。这些板包含大小不同的孔，每个孔可以给出阳性/阴性结果。不同大小的孔类似于不同的稀释液，有助于量化细菌浓度。计数阳性孔，并使用IDEXX表格将孔计数转换为大肠菌群、大肠杆菌和粪肠球菌的MPN计数，这些微生物在废水中含量较高。测试结果表明，再生废水系统中存在微生物再生长。此外，再生水污染了灌溉的植物，并且在废水应用后的前48小时内，污染水平显著降低。