Removal of organic material, nitrogen and phosphorus from wastewater in hybrid subsurface flow constructed wetlands

Abstract

We analysed the performance of one full-size VSSF and HSSF CW and two pilot-scale VSSF and HSSF FS systems in Estonia. We observed in detail the removal of organic material (after BOD7 and CODcr), nitrogen (Ntot) and phosphorus (Ptot) from wastewater (see publications I-IV). This thesis is mainly concentrated on the results that were achieved from November 2005 to December 2006 (divided into 6 periods of various re-circulation regimes), but for background a review of the long-term (January 2007 to May 2008, divided into three working periods) performance of Kodijärve CW is provided. A short overview of experiments performed in the Nõo FS from Aug 2007 to March 2008 is also included. We can conclude that in cold climates it is important to use a VSSF system before the HSSF system, because better aeration of wastewater provides overall better purification efficiency (PE) considering BOD7, CODcr and Ntot removal. It is also necessary not to overload filters in terms of both hydraulic and mass loading rates, so CW and FS dimensions must match the characteristics of the effluent. VSSF and HSSF filters can be designed in an economical way, especially when wastewater re-circulation of 100-300% is applied. The re-circulation of the wastewater improves overall purification significantly. It is possible to achieve satisfactory results in terms of effective BOD and COD removal and nitrification/denitrification as well as Ptot removal. We observed a significant positive correlation between the re-circulation rate and purification efficiency of BOD7, CODcr, Ntot and NH4-N. Käesolevas doktoritöös on analüüsitud ühe täismõõdulise vertikaalvoolulise ja horisontaalvoolulise hübriidse pinnasfiltersüsteemi (Kodijärve) ning kahe vertikaalvoolulise ja horisontaalvoolulise hübriidse piloot- ehk katseseadme (Nõo ja Rämsi) funktsioneerimist reoveepuhastuse eesmärkidel.

Doktoritöö põhjal võime järeldada, et oluline on kasutada vertikaalvoolulist pinnasfiltrit enne horisontaalvoolulist pinnasfiltrit, kuna parem reovee hapnikuga varustatus tagab paremad tulemused puhastusefektiivuste osas, eriti BHT7, KHTcr ja Nüld näitel. Oluline on filtersüsteeme mitte üle koormata ja seda nii hüdrauliliselt kui ka reoainete koormuse osas ehk pinnasfiltersüsteemide dimensioonid peavad vastama neisse juhitava reovee parameetritele.

Vertikaal- ja horisontaalvoolulisi pinnasfiltersüsteeme saab rajada ökonoomselt, eriti juhul kui rakendatakse reovee tagasipumpamist vähemalt määral 100-300% filtritesse juhitud reovee hulgast. Reovee tagasipumpamine parandab üldist puhastusmäära. Võimalik on saavutada rahuldavaid tulemusi BHT ja KHT ärastamise ning nitrifikatsiooni ja denitrifikatsiooni osas.