Wendy C. Quayle

A review of the fate of potassium in the soil–plant system after land application of wastewaters

Irrigation with wastewaters from agri-industry processes such as milk factories, piggeries, wineries and abattoirs is commonplace. These wastewaters all have high levels of potassium (K). Potassium concentration in effluents from domestic wastewater sources are relatively low, reported to vary between 10 and 30 mg L(-1). Higher levels of potassium are reported for effluents from olive oil mills, 10,000-20,000 mg KL(-1), wool scouring, 4200-13,000 mg KL(-1), cheese and lactic whey and potato processing, approximately 1800 mg KL(-1), piggery effluent, 500-1000 mg KL(-1) and winery wastewaters, up to 1000 mg KL(-1). Application of wastewaters with these high potassium levels has been found to increase the overall level of soil fertility, with the exception of alkaline effluents which can dissolve soil organic carbon. Long-term application of such wastewater may cause the build-up of soil potassium and decrease the hydraulic conductivity of the receiving soils. These potential impacts are uncertain and have been inadequately researched. Regulatory limits for potassium in drinking water have been set only by the European Union with no toxicological or physiological justification. The literature shows that grasses and legume herbages accumulate high levels of potassium, up to 5% dry weight, and some grasses, such as turfgrass are particularly tolerant to high levels of potassium, even under saline conditions. This adaptation is considered useful for increasing potassium immobilization and sustainable practices of land wastewater disposal. Potassium availability is significantly affected by the cation ratios of the wastewater, the existing soil water solution and of soil exchange sites.

Phytotoxicity testing of winery wastewater for constructed wetland treatment

Rapid and inexpensive phytotoxicity bioassays for winery wastewater (WW) are important when designing winery wastewater treatment systems involving constructed wetlands. Three macrophyte wetland species (Phragmites australis, Schoenoplectus validus and Juncus ingens) were tested using a pot experiment simulating a wetland microcosm. The winery wastewater concentration was varied (0.5%, 5%, 10%, 25%, 50%, 75% and 100%) and pH was corrected for some concentrations using lime as an amendment. The tolerance of the three aquatic macrophytes species to winery wastewater was studied through biomass production, total chlorophyll and nitrogen, phosphorous and potassium tissue concentrations. The results showed that at greater than 25% wastewater concentration all the macrophytes died and that Phragmites was the least hardy species. At less than 25% wastewater concentration the wetland microcosms were effective in reducing chemical oxygen demand, phenols and total soluble solids. We also evaluated the performance of two laboratory phytotoxicity assays; (1) Garden Cress (Lepidium sativum), and (2) Onion (Allium coepa). The results of these tests revealed that the effluent was highly toxic with effective concentration, EC(50), inhibition values, as low as 0.25%. Liming the WW increased the EC(50) by 10 fold. Comparing the cress and onion bioassays with the wetland microcosm results indicated that the thresholds for toxicity were of the same order of magnitude. As such we suggest that the onion and cress bioassays could be effectively used in the wine industry for rapid wastewater toxicity assessment.

Winery wastewater treatment using the land filter technique

This study outlines a new approach to the treatment of winery wastewater by application to a land FILTER (Filtration and Irrigated cropping for Land Treatment and Effluent Reuse) system. The land FILTER system was tested at a medium size rural winery crushing approximately 20,000 tonnes of grapes. The approach consisted of a preliminary treatment through a coarse screening and settling in treatment ponds, followed by application to the land FILTER planted to pasture. The land FILTER system efficiently dealt with variable volumes and nutrient loads in the wastewater. It was operated to minimize pollutant loads in the treated water (subsurface drainage) and provide adequate leaching to manage salt in the soil profile. The land FILTER system was effective in neutralizing the pH of the wastewater and removing nutrient pollutants to meet EPA discharge limits. However, suspended solids (SS) and biological oxygen demand (BOD) levels in the subsurface drainage waters slightly exceeded EPA limits for discharge. The high organic content in the wastewater initially caused some soil blockage and impeded drainage in the land FILTER site. This was addressed by reducing the hydraulic loading rate to allow increased soil drying between wastewater irrigations. The analysis of soil characteristics after the application of wastewater found that there was some potassium accumulation in the profile but sodium and nutrients decreased after wastewater application. Thus, the wastewater application and provision of subsurface drainage ensured adequate leaching, and so was adequate to avoid the risk of soil salinisation.

Evaluation of the effects of cation combinations on soil hydraulic conductivity

Effects of soil solution cation concentrations and ratios on hydraulic properties must be understood in order to model soil water flow in reactive soils or develop guidelines for sustainable land application of wastewater. We examined effects of different ratios and concentrations of the cations Ca2+, Mg2+, Na+, and K+, using hydraulic conductivity measurements in repacked soil cores, as an indicator of soil structural stability. We examined widely used indices—sodium, potassium, and monovalent cation absorption ratios (SAR, PAR, MCAR)—which assume that the flocculating effects of Ca2+ and Mg2+ are the same, and the dispersive effects of Na+ and K+ are the same. Our laboratory measurements indicate that at any given values of MCAR, the reductions in soil hydraulic conductivity with decrease in electrolyte concentration are not identical for different cation combinations in solution. The hydraulic conductivity curves showed a marked lateral shifting for both the surface and subsurface soils from a winery wastewater application site. This indicates that MCAR is inadequate as a soil stability parameter in soil solutions containing a mixture of Na+, K+, Ca2+, and Mg2+. We employed an unpublished equation that was proposed by P. Rengasamy as a modified index of soil stability for mixed cation combinations, using calculated relative flocculating powers of different cations (‘CROSS’, cation ratio of structural stability). Our observation of lateral shift in hydraulic conductivity measurements at any value of MCAR appears to relate to changes in CROSS values for all cation combinations tested, except for K–Mg solutions, for which a more generalised CROSS equation with modified parameters seems more suitable for calculating the CROSS value. Appropriate modified parameters for use in this generalised CROSS equation were determined empirically, using the experimental data. We derived a combination of threshold electrolyte concentration and CROSS values required to maintain high hydraulic conductivity for the soils at a winery wastewater application site. The potential use of this relationship in developing management practices for sustainable wastewater management at the site is discussed. Further research on the applicability of CROSS and generalised CROSS equations for other soils in the presence of different mixed cation combinations is needed.

Development of a low-cost wastewater treatment system for small-scale wineries.

A pilot-scale winery wastewater treatment system was developed to treat wastewater produced by a small winery (approximately 1200 metric tons of grapes crushed). The pilot system consisted of a sedimentation/aerobic process combined with a bioremediation wastewater cell planted with Juncus ingens. The main design specifications, detailed descriptions of the plant, and analysis of the influent and effluent characteristics (pH, electrical conductivity, total suspended solids, chemical oxygen demand [COD], etc.) are reported for each segment of the system. Over the study period, the mean winery wastewater flowrate was 3.5 m3/d at organic loads of 5000 to 14 000 mg-COD/L. The study measured average removal rates of 72% for COD and 65% for total organic carbon and dissolved carbon. The application of wastewater to the soil increased the soil salinity in the top 30 cm, but remained stable below this. The system also seemed to be effective at neutralizing the pH of the acidic winery wastewater and at removing the phosphorus pool (65%) in the wastewater, whereas the levels of nitrogen and most of the cations increased in the treated effluent. The absorbing/adsorbing and degradation capacity of the soil of the wastewater bioremediation cell did not appear to be exhausted after one vintage. Juncus ingens appeared to grow moderately well, until the end of the vintage, when dieback began to occur. An infilling with organic matter of the surface soil layer under the root zone was observed, which reduced water infiltration and hence system treatment capacity. The data provide evidence that this is a potentially effective wastewater treatment approach for small wineries located in rural areas.

Evaluation of organic matter concentration in winery wastewater: a case study from Australia.

The 5-day biological oxygen demand (BOD(5)) remains a key indicator for proof of compliance with environmental regulators in the monitoring and management of winery effluent. Inter-conversion factors from alternative tests that are more rapid, accurate and simpler to perform have been determined that allow prediction of BOD(5) in winery wastewaters, generally, and at different stages of production and treatment. Mean values obtained from this dataset offer rule of thumb inter-conversion factors: BOD(5) = 0.7 Chemical Oxygen Demand (COD), BOD(5) = 2.3 Total Organic Carbon (TOC) and BOD(5) = 2.7 Dissolved Organic Carbon (DOC). Specific predictive linear relationships are also provided. Out of the relationships between BOD(5) vs COD, TOC and DOC, in winery wastewater, irrespective of vintage or non-vintage production periods and stage of treatment, TOC offered the most reliable prediction of BOD(5). Ethanol, glucose and fructose were evaluated in untreated wastewater as predictors of BOD(5) due to their high specificity in winery effluent. A significant relationship was determined between BOD(5) and (ethanol + glucose + fructose; R(2) = 0.64, n = 19; p<0.05), but relationships between BOD(5) and ethanol and BOD(5) vs (glucose + fructose) were weak (R(2) = 0.45 and 0.34; n = 19; p<0.05 respectively,). There was a very strong linear correlation (y = 0.9767x + 52.8; R(2) = 0.97; n = 23; p<0.05) in COD data in winery effluents when using a commercially available mercury free test kit compared with using a traditional COD test kit that contained mercury. This suggests that mercury free COD test kits could be used by the wine industry for organic pollution assessment with associated reductions to user and environmental risk, as well as reducing the costs of kit waste disposal.

Assessment of In-Season Cotton Nitrogen Status and Lint Yield Prediction from Unmanned Aerial System Imagery

The present work assessed the usefulness of a set of spectral indices obtained from an unmanned aerial system (UAS) for tracking spatial and temporal variability of nitrogen (N) status as well as for predicting lint yield in a commercial cotton (Gossypium hirsutum L.) farm. Organic, inorganic and a combination of both types of fertilizers were used to provide a range of eight N rates from 0 to 340 kg N ha−1. Multi-spectral images (reflectance in the blue, green, red, red edge and near infrared bands) were acquired on seven days throughout the season, from 62 to 169 days after sowing (DAS), and data were used to compute structure- and chlorophyll-sensitive vegetation indices (VIs). Above-ground plant biomass was sampled at first flower, first cracked boll and maturity and total plant N concentration (N%) and N uptake determined. Lint yield was determined at harvest and the relationships with the VIs explored. Results showed that differences in plant N% and N uptake between treatments increased as the season progressed. Early in the season, when fertilizer applications can still have an effect on lint yield, the simplified canopy chlorophyll content index (SCCCI) was the index that best explained the variation in N uptake and plant N% between treatments. Around first cracked boll and maturity, the linear regression obtained for the relationships between the VIs and both plant N% and N uptake was statistically significant, with the highest r2 values obtained at maturity. The normalized difference red edge (NDRE) index, and SCCCI were generally the indices that best distinguished the treatments according to the N uptake and total plant N%. Treatments with the highest N rates (from 307 to 340 kg N ha−1) had lower normalized difference vegetation index (NDVI) than treatments with 0 and 130 kg N ha−1 at the first measurement day (62 DAS), suggesting that factors other than fertilization N rate affected plant growth at this early stage of the crop. This fact affected the earliest date at which the structure-sensitive indices NDVI and the visible atmospherically resistant index (VARI) enabled yield prediction (97 DAS). A statistically significant linear regression was obtained for the relationships between SCCCI and NDRE with lint yield at 83 DAS. Overall, this study shows the practicality of using an UAS to monitor the spatial and temporal variability of cotton N status in commercial farms. It also illustrates the challenges of using multi-spectral information for fertilization recommendation in cotton at early stages of the crop.