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Monitoring and performance evaluation of pilot Horizontal Sunsurface Flow Constructed Wetlands treating olive mill wastewater

Moschogianni Dimitra

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Summary

The present thesis investigated the monitoring and performance of four pilot-scale constructed wetlands with horizontal subsurface flow which aim to reduce organic load and remove nutrients and other pollutants from the wastewater of a three-phase olive mill, without additional processes, as well as to draw conclusions based on experimental measurements for the validity of their design and effectiveness.The followed method involves four units of constructed wetlands of horizontal subsurface flow with a volume of 188 litres, which were placed in the open space of Technical University of Crete in Chania, with the following filling mediums: the first unit does not contain any vegetation and it is filled with zeolite and expanded clay (Leca) symbolized as "C", while in the next three units the common reed Phragmites australis has been planted and contain the following filling materials: the second unit contains zeolite and expanded clay symbolized as "ZL", the third recycled plastic (HDPE) and biochar symbolized as "PB", and the fourth only recycled plastic symbolized as "P".The units were loaded at specific intervals with different quantities of liquid waste from an olive mill, which originated from a three-phase olive mill in the area of Perivolia in Chania, specifically from the phase of simple drainage into a closed tank of all the liquid fraction produced during the centrifugation of three phases. Specifically, prior to loading the units, the liquid waste from the olive mill was diluted with water in a ratio of 1:8. Additionally, at regular intervals, samples were collected from the inflow and outflow of the units, and the necessary photochemical analyses were carried out in the laboratory to study their performance. Specifically, the following parameters were measured in the laboratory: pH, conductivity (EC), BOD5, COD, colour (TCU), NO3--N, NH4+-N, total nitrogen TN, PO43--P, total phosphorus TP, total phenols, and total suspended solids TSS.This study examined the effectiveness of constructed wetlands in wastewater treatment and environmental protection. The results provided important insights into system design and the efficiency of each horizontal flow unit (C, ZL, P, and PB). More specifically, the results showed that unit C achieved a removal efficiency of 63 ± 19% for COD, 90 ± 6% for BOD5, 86 ± 7% for total phenols, 52 ± 30% for TSS, 82 ± 12% for TN, 94 ± 7% for TP, and 81 ± 7% for color removal. The ZL unit, which had the same filling materials as unit C but included vegetation, achieved removal efficiencies of 64 ± 19% for COD, 90 ± 10% for BOD5, 86 ± 8% for total phenols, 59 ± 27% for TSS, 84 ± 7% for TN, 94 ± 8% for TP, and 81 ± 7% for color removal.Furthermore, unit P demonstrated removal efficiencies of 50 ± 22% for COD, 60 ± 24% for BOD5, 45 ± 18% for total phenols, 52 ± 17% for TSS, 46 ± 26% for TN, and 35 ± 22% for TP, while no significant color removal was observed. Finally, unit PB exhibited removal efficiencies of 51 ± 23% for COD, 63 ± 25% for BOD5, 48 ± 20% for total phenols, 64 ± 21% for TSS, 49 ± 23% for TN, and 33 ± 23% for TP, with no observed color removal in this case as well.Based on the results, it can be concluded that the C and ZL units, which use zeolite and leca as filling materials, exhibit high performance in treating olive mill wastewater, with the ZL unit showing slightly better results due to the inclusion of the Phragmites australis plant.The P and PB units, which use HDPE and biochar as filling materials, achieved adequate removal rates for certain pollutants but did not perform as efficiently as the C and ZL units.In conclusion, Constructed Wetlands represent a sustainable and environmentally friendly solution for the treatment of olive mill wastewater, contributing to pollution reduction and to sustainable utilization of natural resources through innovative design approaches.

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