Dear Megan, I read some ...

Dear Megan,

I read some comments to your quetsion and I want to clarify some concepts for you and for the readers, on the basis of my expertise. From my point of view, horizontal flow CWs is fine for your purposes. Firstly, it's not true that HF are more prone to clogging,  if you properly design the transversal inlet area (see Treatment Wetlands 2nd edition - Kadlec and Wallace, for more details) the risk of clogging is lower than VF, since you use coarser material (gravel) instead of the sand used in the VF. Secondly, it's not true that HF are used only for denitrification; HF provides some benefits in comparison to VF, especially in terms of simpler functioning (no needs of pumps or syphons if you have good horographic), this also means that you need less O&M activities and costs.  Moreover, HF works in more or less "plug-flow", with higher hydraulic retention time in comparison to VF, therefore you have more time to create contact within roots and greywater, helping to let me say find  carbon or nitrogen (in greywater you can have excess of both C and N, depending from which sources you take the grey water and if people pee in the shower) "somewhere" to have proper balance of C:N for biofilm, issue often encountered in compact activated sludge reactor used for grey water, and possible also for VF. The drawbacks of HF in comparison to VF are mainly 2: i) the less TSS removal, which you can tackle with a second VF stage, depending of the type of reuse you want (for simple irrigation is enough HF, for reuse in toilet flush it could be advisable to use also a VF) and the size of your system; ii) environmental, since HFs are mainly anoxic/anaerobic, and produce higher amount of methane (a greenhouse gas) in comparison to VF.

Cheers