Phytoremediation performance of floating treatment wetlands with pelletized mine water sludge for synthetic greywater treatment

Abstract

Purpose Buckets containing floating reed (Phragmites australis) simulated floating treatment wetlands (FTWs) and were used to improve the remediation performance of synthetic greywater (SGW). The aim of the study was to investigate the behaviour of FTWs for treatment of key contaminants within artificial greywater. Methods Pelletized ochre based on acid mine water sludge was introduced to selected FTWs, because of its capability in sequestration phosphorus and other trace elements. The impact of the following four operational variables were tested in the experimental set-ups of the FTWs (four replicates each): pollutant strength (high-(HC) and low-(LC) concentrations), treatment time (2-or 7-days of hydraulic retention time (HRT)), presence or absence of macrophytes (P. australis) and cement-ochre pellets.Results The results showed that 5 − day biochemical oxygen demand (BOD) and chemical oxygen demands (COD) were significantly (p < 0.05) reduced in all wetlands. Nitrate-nitrogen (NO 3 -N) concentrations were significantly (p < 0.05) higher, and those measurements for PO 4 -P were significantly (p < 0.05) lower than the corresponding ones determined for the influent. The existence of ochre pellets with P. australis significantly (p < 0.05) decreased B, Cd, Cr, Cu, Mg, Ni and Zn concentrations, but increased Al, Ca, Fe and K concentrations in the effluent, with the exception of sodium (Na). Conclusions The FTW performances can be improved by utilising ochre-cement pellets to increase the pH of greywater. The presence of P. australis acts as a buffer to neutralise the pH of SGW. Rhizomes and biofilms mitigate increases in turbidity, TSS and colour values.

Impact of Storage Time on Characteristics of Synthetic Greywater for Two Different Pollutant Strengths to Be Treated or Recycled

“…Microbial degradation processes are the principle reason for the consumption of organic matter, which leads to higher respiration and therefore to an increase in BOD 5 (Friedler et al 2006;Maiga et al 2014). It is possible that the drops in BOD 5 were also caused by sedimentation, since, BOD 5 statistically correlated with TSS (Abed et al 2019). The statistical evaluation in Table 3 shows that there was no significant effect (p > 0.05) when extending the storage time by more than 2 days on the BOD 5 values.…”

“…The BOD 5 to COD ratio for HC-greywater decreased, reaching 0.14 at 2 days and 0.16 at 7 days of storage. Greywater of low strength, which commonly originates from hand-washing basins and showers, has shown low concentrations of BOD 5 and COD (Avery et al 2007;Jefferson et al 2004;Abed et al 2019).…”

“…Sedimentation might not be a straight-forward physical process concerning trace element removal, except if they are part of large suspended particles. Other processes like complexation, precipitation and co-precipitation might have to happen first (Abed et al 2019).…”

“…Dissolved metal precipitation could occur when binding inorganic contaminants in various chemical reactions to the sediment and colloid surfaces through adsorption processes (Hua et al 2012). The process of sedimentation becomes possible only after floc formation (Abed et al 2017(Abed et al , 2019. With the development of a blanket of flocs, which have surface electronic charges, sedimentation of fine pollutant particles becomes likely (Hua et al 2012).…”

“…Storing and reusing of greywater are linked to a risk of spreading diseases due to the possibility of pathogen presence. Nevertheless, this risk is significantly less than for black water comprising predominantly domestic wastewater (Eriksson et al 2002;Abed et al 2019). It has been indicated that a significant number of bacteria have grown when greywater was stored for 72 h (March and Gual 2009;Abdel-Shafy et al 2019).…”