Anna Crolla

Pollutant removal from municipal sewage lagoon effluents with a free-surface wetland

This research project was initiated to refine the knowledge available on the treatment of rural municipal wastewater by constructed wetlands. To determine the treatment capacity of a constructed wetland system receiving municipal lagoon effluents, the wetland was monitored over one treatment season, from May 19 to November 3, 2000. The wetland system consisted of a three-cell free-surface wetland, phosphorus adsorption slag filters and a vegetated filter strip. Bimonthly water samples at the inlet and outlet of each component of the wetland system were analysed for biochemical oxygen demand, nitrate and nitrite, ammonia and ammonium, total Kjeldahl nitrogen (TKN), total suspended solids (TSS), total phosphorus (TP), ortho-phosphate (ortho-PO(4)), fecal coliforms (FCs) and Escherichia coli. The free-surface wetland cells treating the lagoon effluents achieved removals as follows: biochemical oxygen demand (34%), ammonia and ammonium (52%), TKN (37%), TSS (93%), TP (90%), ortho-PO(4) (82%), FCs (52%) and E. coli (58%). The wetland cells reduced total nitrogen, TP and biochemical oxygen demand to levels below the maximum permissible levels required for direct discharge to nearby receiving waters (TN<3.0 mg x L(-1), TP<0.3 mg x L(-1), BOD(5)<3.0 mg x L(-1)). The vegetated filter strip treating the effluents from the wetland cells achieved removals as follows: biochemical oxygen demand (18%), ammonia and ammonium (28%), TKN (11%), TSS (22%), TP (5%), FCs (28%) and E. coli (22%). It may therefore serve as an additional treatment stage further reducing the concentrations of these mentioned parameters. The slag filters reduced TP in the lagoon effluents by up to 99%, and, in this study, were concluded to be effective phosphorus adsorbers.

Statistical modelling of the impact of some polyphenols on the efficiency of anaerobic digestion and the co-digestion of the wine distillery wastewater with dairy cattle manure and cheese whey.

The objective of this study was to determine the effectiveness of anaerobic digestion in the treatment of polyphenols (PP) present in olive mill wastewater (OMW) and wine distillery wastewater (WDW). Anaerobic Toxicity Assay (ATA) was conducted to assess the impact of the most representative phenolic compounds present in OMW and WDW: catechol, tannins and p-Coumaric acid, on biogas production. The results from this study show that tannins do not present any inhibitory effect on methanogenesis at a concentration level of 1,664 ppm, whereas catechol has an inhibitory effect at 1,664 ppm. In addition, p-Coumaric acid was strongly inhibitory at 50 ppm. The co-digestion of OMW and WDW with other effluents was proposed as a solution for reducing the load of PP in the anaerobic medium. Biochemical methane potential (BMP) tests were carried out for dairy cattle manure and mixtures of five PP. A central composite design was implemented on the BMP tests to model the biogas production response and the degradation kinetics of PP. The co-digestion of WDW with cattle manure and/or whey was also investigated in BMP tests. The results show that the digestion was optimal at a ratio of 16: 64: 20 (WDW: manure: inoculum) with a maximum biogas yield of 172 mL/g of VS and 66% COD removal.

Methane emissions from digestate at an agricultural biogas plant.

Methane (CH4) emissions were measured over two years at an earthen storage containing digestate from a mesophilic biodigester in Ontario, Canada. The digester processed dairy manure and co-substrates from the food industry, and destroyed 62% of the influent volatile solids (VS). Annual average emissions were 19gCH4m(-3)d(-1) and 0.27gCH4kg(-1)VSd(-1). About 76% of annual emissions occurred from June to October. Annual cumulative emissions from digestate corresponded to 12% of the CH4 produced within the digester. A key contributor to CH4 emissions was the sludge layer in storage, which contained as much VS as the annual discharge from the digester. These findings suggest that digestate management provides an opportunity to further enhance the benefits of biogas (i.e. reducing CH4 emissions compared to undigested liquid manure, and producing renewable energy). Potential best practices for future study include complete storage emptying, solid-liquid separation, and storage covering.

Land application of digestate

Abstract: The anaerobic digestion process involves the breakdown of organic matter to produce biogas, a mixture of CH4 and CO2 gases. During this process, nutrients are transformed, volatile fatty acids are consumed and pathogens reduced, leading to potential environmental and agronomic benefits associated with the land application of digestate. An extensive examination of the effects of land application of digestate on NH3 and N2O emissions, odour emissions, crop yield and migration of NO3‒–N and bacteria to drainage tiles is presented. Experimental field data collected by the authors supporting these environmental and agronomic impacts are referenced throughout the chapter.

Potential methane emission reductions for two manure treatment technologies

ABSTRACT The effect of two dairy manure treatments, solid–liquid separation (SLS) and anaerobic digestion (AD), on methane potential and the speed of production was evaluated. Assays were performed in the lab to measure methane (CH4) production over 202 d from dairy manure samples taken before and after each treatment. Compared to raw manure, CH4 emissions on a per-L basis were reduced 81% by SLS and 59% by AD, on average. The mean (SD) ultimate CH4 emission potential (B0) per kg of volatile solids (VS) was 247 (8) L CH4 kg−1 VS for raw manure, 221 (9) L CH4 kg−1 VS for separated liquid, and 160 (4) L CH4 kg−1 VS for anaerobic digestate. Thus, SLS reduced the B0 of the liquid fraction by 11% and AD reduced B0 by up to 35% compared to raw manure. Manure treatment affected the speed of CH4 production: SLS increased the CH4 production rate and thus separated liquid manure was the fastest to produce 90% of the ultimate CH4 production. Therefore, both the speed of degradation and B0 should be considered when assessing these techniques for farm-scale manure storages, because actual emission reductions will depend on storage conditions.

Characterizing the Performance of Gas-Permeable Membranes as an Ammonia Recovery Strategy from Anaerobically Digested Dairy Manure

Capturing ammonia from anaerobically digested manure could simultaneously decrease the adverse effects of ammonia inhibition on biogas production, reduce reactive nitrogen (N) loss to the environment, and produce mineral N fertilizer as a by-product. In this study, gas permeable membranes (GPM) were used to capture ammonia from dairy manure and digestate by the diffusion of gaseous ammonia across the membrane where ammonia is captured by diluted acid, forming an aqueous ammonium salt. A lab-scale prototype using tubular expanded polytetrafluoroethylene (ePTFE) GPM was used to (1) characterize the effect of total ammonium nitrogen (TAN) concentration, temperature, and pH on the ammonia capture rate using GPM, and (2) to evaluate the performance of a GPM system in conditions similar to a mesophilic anaerobic digester. The GPM captured ammonia at a rate between 2.2 and 6.3% of gaseous ammonia in the donor solution per day. Capture rate was faster in anaerobic digestate than raw manure. The ammonia capture rate could be predicted using non-linear regression based on the factors of total ammonium nitrogen concentration, temperature, and pH. This use of membranes shows promise in reducing the deleterious impacts of ammonia on both the efficiency of biogas production and the release of reactive N to the environment.

Field Nitrogen Losses Induced by Application Timing of Digestate from Dairy Manure Biogas Production.

Anaerobic digestion of dairy manure has environmental benefits, but the impact of effluent (i.e., digestate [DG]) application on environmental nitrogen (N) losses from soils has not been well quantified. Our objective was to evaluate how field application of DG affected nitrous oxide (NO) emissions and nitrate (NO) leaching compared with raw dairy manure (RM) in spring versus fall applications. We measured N losses year-round for 2.5 yr in silage corn on tile-drained clay soil in Alfred, Ontario, Canada. Treatments were: digestate applied in spring (DS) and fall (DF), raw dairy manure applied in spring (RS) and fall (RF), urea applied in spring, and a control. Overall, the source of N had no effect on annual NO emissions (overall average DG and RM, 4.9 kg NO-N ha yr), but more NO leached from DS than RS treatments (8.8 and 4.8 kg NO-N ha yr on average, respectively). Estimated indirect NO emissions from leached NO-N were small (<0.2 kg NO-N ha yr). Timing of application did not affect annual NO emissions but did shift emissions to the non-growing season for fall applications (65% on average) and to the growing season for spring applications (60% on average). Overall environmental N losses (NO-N + NO-N) from DG were similar to RM when applied at the same time. For the conditions of our study, downstream emissions from anaerobic digestion (i.e., emissions induced by applied digestate) do not present an adverse trade-off to the environmental benefits incurred during the biogas production phase.

Treatment of potato farm wastewater with sand filtration.

ABSTRACT This study examined sand filtration as a component of a potato farm wastewater treatment system. Two different sand filter designs, saturated flow and unsaturated flow, were evaluated at three different loading rates: 34, 68, and 136 L m−2 d−1. Filter design had a significant effect, with unsaturated flow sand filters having significantly (p < .05) better total suspended solids (TSS) removal (89%) than saturated flow sand filters did (79%). Loading rate also had a significant (p < .05) effect, given that the lowest loading rate had higher mass removal for TSS than the higher loading rates did. Overall, all sand filters removed TSS, 5-d biochemical oxygen demand, and total phosphorus well (62–99%). Total nitrogen removal was twice as high in unsaturated flow filters (53%) than in saturated flow filters (27%), because of the recurring cycle of aerobic and anaerobic conditions during sand saturation and drying in unsaturated flow sand filters.

A combined reed bed/freezing bed technology for septage treatment and reuse in cold climate regions

A combined reed bed-freezing bed (RB-FB) technology was effective at treating septage under Canadian climatic conditions over a 5-year period with average loading rates of 82-104 kg TS/m2/y. Varying hydraulic and solid loading rates as well as the increasing sludge cake with time had little to no effect on treatment efficiency, with almost complete removal of organic matter, solids, heavy metals and nutrients. Filtrate concentrations varied significantly between the freeze-thaw and growing seasons for many parameters, although the differences were not important from a treatment or reuse perspective with filtrate quality similar to a low to medium strength domestic wastewater. The potential to reuse the filtrate as a source of irrigation water will depend upon local regulations. The dewatered sludge cake consistently met biosolids land application standards in terms of pathogen and metals content, with Escherichia coli numbers declining with time as sludge cake depth increased. A combined RB-FB technology can provide a cost-effective solution for septage management in northern rural communities with potential for beneficial reuse of both the filtrate and dewatered sludge cake.

Ammonia removal from poultry manure leachate via struvite precipitation: a strategy for more efficient anaerobic digestion

To improve poultry waste management, the feasibility of enabling efficient anaerobic digestion of poultry manure through reduction of ammonia accumulation is examined. This study employs struvite precipitation to control ammonia accumulation, and focuses on the efficacy of ammonia removal under neutral reaction conditions (pH = 7). The impacts of phosphate and magnesium additives, pH, temperature and the N:Mg:P molar ratio are quantified. Magnesium chloride (MgCl2 • 6H2O) and monopotassium phosphate (KH2PO4) are shown to be the most efficient combination of additives for total ammoniacal nitrogen (TAN) reduction of poultry manure leachate under neutral reaction conditions (pH = 7), demonstrating a TAN reduction of 90.3%. Modification of molar ratios (NH4:Mg:PO4) evidenced no significant benefit with regard to TAN reduction. However, increasing the fraction of supplementary magnesium resulted in a statistically significant (p < 0.05) decrease in phosphate concentration within the leachate. This study demonstrates the advantages of struvite precipitation, as a method of ammonia control, to improve anaerobic digestion and hence management of poultry manure. Although an effective means of TAN control, struvite precipitation from poultry manure is an ineffective means of obtaining pure struvite due to the formation of co-precipitates.