Abstract
Reject water is a by-product of every municipal and agro-industrial wastewater treatment plant (WWTP) applying sewage sludge stabilization. It is usually returned without pre-treatment to the biological part of WWTP, having a negative impact on the nitrogen removal process. The current models of pollutants removal in constructed wetlands concern municipal and industrial wastewater, whereas there is no such model for reject water. In the presented study, the results of treatment of reject water from dairy WWTP in subsurface vertical flow (SS VF) and subsurface horizontal flow (SS HF) beds were presented. During a one-year research period, SS VF bed reached 50.7% efficiency of TN removal and 73.8% of NH4+-N, while SS HF bed effectiveness was at 41.4% and 62.0%, respectively. In the case of BOD5 (biochemical oxygen demand), COD (chemical oxygen demand), NH4+-N, and TN (total nitrogen), the P-k-C* model was applied. Multi-model nonlinear segmented regression analysis was performed. Final mathematical models with estimates of parameters determining the treatment effectiveness were obtained. Treatment efficiency increased up to the specific temperature, then it was constant. The results obtained in this work suggest that it may be possible to describe pollutant removal behavior using simplified models. In the case of TP (total phosphorus) removal, distribution tests along with a t-test were performed. All models predict better treatment efficiency in SS VF bed, except for TP.
Highlights
In Europe, the biggest municipal and agro-industrial wastewater treatment plants (WWTPs) utilize anaerobic sewage sludge digestion with biogas production [1]
One of the major problems connected with anaerobic digestion chamber exploitation is reject water, which is generated in the process of dewatering stabilized sewage sludge
It is usually returned without pre-treatment to the biological part of a WWTP, having a negative impact on the treatment process and causing problems with reaching high effectiveness of nitrogen removal [2,3,4]
Summary
In Europe, the biggest municipal and agro-industrial wastewater treatment plants (WWTPs) utilize anaerobic sewage sludge digestion with biogas production [1]. The possibility of heat and electric energy production from biogas is an advantage of such sewage sludge treatment, which decreases the cost of waste treatment significantly. One of the major problems connected with anaerobic digestion chamber exploitation is reject water, which is generated in the process of dewatering stabilized sewage sludge. It is usually returned without pre-treatment to the biological part of a WWTP, having a negative impact on the treatment process and causing problems with reaching high effectiveness of nitrogen removal [2,3,4]. The problem of reject water treatment in a conventional sludge
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