# Preliminary Study on Greywater Treatment Using Nonwoven Textile Filters
## 4 Discussion
The basic processes occurring during greywater treatment on non-woven filters were: the removal of organic contaminants, determined as \(\text{BOD}_{5}\), \(\text{COD}_{\text{Cr}}\), and total phosphorus. However, the removal of the latter ones proved to be unstable. The beneficial effect accompanying the decrease in filter outflow rate was the increased and more stable removal efficiency [34]. Decrease of the flow rate of filters with a lowering of the greywater surface level is unfavorable from the point of view of their hydraulic efficiency (capacity), but it is of some advantage in terms of operation. At a reduced inflow rate or lack of greywater inflow (several days), greywater of about 10-15 cm depth remains in the reactor and \"sustains\" the conditions of \begin{table}
\begin{tabular}{c c c c} \hline
**Parameter** & **Type of Treatment** & **Statistical Test** & \(\boldsymbol{p}\) \\ \hline \multirow{4}{*}{COD efficiency removal (\%)} & Set I (filter 1 and filter 2) & Paired & 0.46 \\  & Set II (filter 1 and filter 5) & wilcox.test & 0.87 \\  & Filter 1 of set I and filter 1 of set II & Wilcox.test & 0.46 \\ \(\text{BOD}_{5}\) efficiency removal (\%) & Set I (filter 1 and filter 2) & Paired.t.test & 0.28 \\  & Set I (filter 1 and filter 2) & Paired & 0.67 \\ \(\text{P}_{\text{tot}}\) efficiency removal (\%) & Set II (filter 1 and filter 5) & Paired.t.test & 0.76 \\  & Filter 1 of set I and filter 1 of set II & Wilcox.test & 0.23 \\  & Set I (filter 1 and filter 2) & Paired.t.test & 0.5 \\ \(\text{COD}\) outflow (mg dm\({}^{-3}\)) & Set II (filter 1 and filter 5) & Paired.t.test & 0.79 \\  & Filter 1 of set I and filter 1 of set II & t.test & 0.4 \\ \(\text{BOD}_{5}\) outflow (mg dm\({}^{-3}\)) & Set I (filter 1 and filter 2) & Paired & 0.47 \\  & Set I (filter 1 and filter 2) & Paired & 0.53 \\ \(\text{P}_{\text{tot}}\) outflow (mg dm-3) & Set II (filter 1 and filter 5) & Paired & 0.79 \\  & Filter 1 of set I and filter 1 of set II & Wilcox.test & 0.004 * \\ \hline \end{tabular} (*) The significant difference at 95% confidence interval.  
\end{table} 
Table 1: The result of statistical test. biomass existence in the low located zone of the filters and causes capillary infiltration at the height of several centimeters. Regardless of how the filters are fed, their filtration velocity after several months of operation can be estimated as 1-1.4 cm d\({}^{-1}\), which with an average greywater volume of 25-40 dm\({}^{3}\) from one person during 24 h means a demand of 1.8-4.0 m\({}^{2}\) of filter surface area per person, and from 7.1 to 16 m\({}^{2}\) for a four-person family. For four persons, between 9 and 20 filters are needed (with plan view dimensions: 1.0 x 0.01 m, height 0.4 m, and filter surface area of a single filter of 0.8 m\({}^{2}\)). The filters have a large ratio of filter material surface to volume of treated greywater, thus diffusing oxygen from atmospheric air to greywater--where it runs in a sufficiently intensive manner so that forced (artificial) aeration is not necessary for the greywater. The filters can therefore work practically with very low energy consumption (related to greywater pumping only)--less than 0.5 kWh m\({}^{-3}\) (several times per day for a period of several seconds using pump of power 400 watt). Mechanical-biological treatment technology on non-woven filters allows also to capture the suspended solids outflowing from household and prevent a soil absorption system from clogging.