Evaluating the performance of horizontal subsurface flow constructed wetlands using natural zeolite (escott)

The objective of the present study was to assess the simultaneous removal of physiochemical parameters in moderate strength wastewater using a lab scale horizontal subsurface flow constructed wetland (HFCW) with natural zeolite as a substrate. In this study, high-density polyethylene tanks (0.36 m²) were planted with phragmites australis and scirpus maritimus and received 0.012 m³/d to 0.08 m³/d of synthetic wastewater corresponding to a HLR of 0.035 to 0.243 m/d and a COD loading rate of 0.0148 kg COD (m².d)^-1 to 0.026 kg COD (m².d)^-1. The HFCW was subjected to three hydraulic retention times (HRT) for 4, 3 and 2 days respectively. Averaged data reported coincided with the plant age (4 to 55 weeks) and covered the entire cold season and early part of the hot season. Based on the 55 weeks of operation, the HFCW unit with zeolite achieved significantly higher removal for COD (85 to 88%), TN (54 to 96%), NH₄-N (50 to 99%) and TSS (91 to 96%) respectively at all HRT. This system was proved to be tolerant to high organic loadings and nutrients, suggesting these substrates as viable options for biological treatment of wastewater.

Evaluating the performance of different media in a horizontal subsurface flow constructed wetland

The treatment efficiency of a wetland system requires a balance between pollutant loading rate and hydraulic retention time (HRT), hydraulic loading rate (HLR) and the suitable substrate to be used. The aim of this study was to investigate the treatment efficiency of horizontal subsurface flow constructed wetland planted with phragmites australis and scirpus maritimus containing three different substrates to treat agricultural wastewater under short term operation. Alum sludge and zeolite were used as substrates and gravel was used as a control for a laboratory-scale horizontal flow constructed wetland (CW) units that were made of high-density Polyethylene. The units were operated under 2, 3 and 4 days of HRTs and at different HLR for each substrate. Each beds received 0.012 m3/d to 0.08 m3/d of synthetic wastewater corresponding to a HLR of 0.035 to 0.243 m/d and a COD loading rate of 0.0148 kg COD (m2.d)-1 to 0.026 kg COD (m2.d)-1. The relationships between the substrate, retention time and removal efficiency, especially of organic matter and nutrient removal were investigated. All units showed relatively stable removal for COD during the entire operational period. The COD removal for all units and HRT were in ranged from 67% to 93%. The zeolite unit achieved significantly higher removal of TN, NH4-N and TSS compared to alum sludge and gravel unit at all HRT. The unit with zeolite was highly effective in removing TN (54 to 96%), NH4-N (50 to 99%) and TSS (91 to 96%) respectively, at 2, 3 and 4 days of HRT. Meanwhile, alum sludge was highly effective in removing phosphate. The removal of phosphate from alum sludge unit was ranged from 94 to 97% for all HRT. Compared to gravel CW unit, zeolite and alum sludge CW were proved to be tolerant to high organic loadings and nutrients, suggesting these substrates as viable options for biological treatment of agricultural wastewater.

Evaluation of the giant reed (Arundo donax) in horizontal subsurface flow wetlands for the treatment of dairy processing factory wastewater

Two emergent macrophytes, Arundo donax and Phragmites australis, were established in experimental horizontal subsurface flow (HSSF), gravel-based constructed wetlands (CWs) and challenged by treated dairy processing factory wastewater with a median electrical conductivity of 8.9 mS cm−1. The hydraulic loading rate was tested at 3.75 cm day−1. In general, the plants grew well during the 7-month study period, with no obvious signs of salt stress. The major water quality parameters monitored (biological oxygen demand (BOD), suspended solids (SS) and total nitrogen (TN) but not total phosphorus) were generally improved after the effluent had passed through the CWs. There was no significance different in removal efficiencies between the planted beds and unplanted gravel beds (p > 0.007), nor was there any significant difference in removal efficiencies between the A. donax and P. australis beds for most parameters. BOD, SS and TN removal in the A. donax and P. australis CWs was 69, 95 and 26 % and 62, 97 and 26 %, respectively. Bacterial removal was observed but only to levels that would allow reuse of the effluent for use on non-food crops under Victorian state regulations. As expected, the A. donax CWs produced considerably more biomass (37 ± 7.2 kg wet weight) than the P. australis CWs (11 ± 1.4 kg wet weight). This standing crop equates to approximately 179 and 68 tonnes ha−1 year−1 biomass (dry weight) for A. donax and P. australis, respectively (assuming a 250-day growing season and single-cut harvest). The performance similarity of the A. donax and P. australis planted CWs indicates that either may be used in HSSF wetlands treating dairy factory wastewater, although the planting of A. donax provides additional opportunities for secondary income streams through utilisation of the biomass produced.

Process-based modelling of mass transport in the subsurface

Modern societies rely on natural water pathways that include subsurface flow of water and dissolved chemicals. The thesis presents a range of numerical and analytical models for simulating physical, chemical and biological processes in the subsurface, including coastal aquifers, the near-surface vadose zone, and solute transport in biogeochemically active aquifers.

Performance of the Giant Reed (Arundo donax) in experimental wetlands receiving variable loads of industrial stormwater

Two emergent macrophytes, Arundo donax and Phragmites australis, were established in experimental subsurface flow, gravel-based constructed wetlands (CWs) and challenged by untreated stormwater collected from the hard-pan and other surfaces of a dairy processing factory in south-west Victoria, Australia. The hydraulic loading rate was tested at two levels, sequentially, 3.75 and 7.5 cm day -1. Some of the monitored variables were removed more efficiently by the planted beds in comparison to unplanted CWs (biochemical oxygen demand (BOD), total nitrogen (TN) and total phosphorus (TP); p<0.007) but there was no significant difference between the A. donax and P. australis CWs in removal of BOD, suspended solids (SS) and TN (p>0.007) at 3.75 cm day -1 or SS and TN at 7.5 cm day -1. At 3.75 cm day -1, BOD, SS, TN and TP removal in the A. donax and P. australis CWs was 71%, 61%, 78% and 75% and 65%, 60%, 73% and 41%, respectively. Nutrient removal at 7.5 cm day -1 in the A. donax and P. australis beds was 87%, 91%, 84% and 71% and 96%, 94%, 87% and 55%, respectively. As expected, the A. donax CWs produced considerably more biomass (10±1.2 kg wet weight) than the P. australis CWs (2.7±1.2 kg wet weight). This equates to approximately 107 and 36 tonnes ha -1 year -1 biomass (dry weight) for A. donax and P. australis, respectively (assuming 250 days of growing season and singlecut harvest). The performance similarity of the A. donax- and P. australis-planted CWs indicates that either may be used in HSSF wetlands treating dairy factory stormwater, although the planting of A. donax provides additional opportunities for secondary income streams through utilisation of the biomass produced.

Constructed wetland for treating aquaculture and industrial effluent

This project was a practical assessment of the giant reed Arundo donax in comparison with the common reed, Phragmites autralis, in gravel substrate-based horizontal subsurface flow constructed wetlands designed to treat agro-industrial effluent. Results indicated, the planted CWs were more effective at removing nutrients than the unplanted conrol CWs with A.donax produce larger amounts of biomass than P. australis planted CWs.