Evaluation and optimisation of chemical treatment for non-point source pollution control:purification of peat extraction runoff water

Abstract Chemical treatment is considered best available technology for purification of peat extraction runoff in Finland, due to its capability to remove dissolved organic carbon (DOC), suspended solids and nutrients. However, lack of optimisation and adaptation of this method for purification of diffuse pollution sources, e.g., peat extraction runoff, has led to significant fluctuations in purification efficiency. This thesis evaluated the suitability of commercially available coagulants for the treatment of typically humic water. Inorganic (ferric sulphate, aluminium sulphate and a mixed product) and organic (polyDADMAC, polyamine, chitosan and tannin products) coagulants were studied. Investigations included assessment of required dosage and the influence of process parameters (pollutant concentration, mixing, water pH and temperature) on coagulant performance. In addition, the process conditions in existing treatment systems were examined in field experiments aimed at identifying possible factors affecting purification. Ferric sulphate (FS) was the most effective of the coagulants tested. It produced excellent flocs and achieved higher removal efficiency, particularly for DOC, than the other coagulants. However, the dosage required for FS was significantly higher than for e.g., polyDADMAC and chitosan. Moreover, samples treated with FS displayed high iron concentration and acidic pH. The organic polymers achieved satisfactory results, but further research is needed before they can become viable alternatives to metal salts. The quality of peat extraction runoff water was found to vary significantly. It was also observed that variations in DOC concentration, even for particulate rich samples, controlled coagulant dosage and, consequently, treatment efficiency. For inorganic coagulants, mixing provided during flocculation had a more significant influence on purification than mixing provided during coagulation. This is relevant hence in now existing treatment facilities no mixing is employed during flocculation. Based on the research conducted, suggestions were formulated for process optimisation aimed at reducing variations in purification efficiency, thus increasing the reliability of the method and reducing related environmental impacts.Tiivistelmä Turvetuotannon valumavesien käsittelyssä yksi parhaista käyttökelpoisistatekniikoista on kemiallinen käsittely, koska se pystyy poistamaan valumavedestä liukoista orgaanista hiiltä (DOC), kiintoainetta ja ravinteita. Tästä huolimatta kemiallisen käsittelyn optimointia ei ole tehty hajakuormitukselle, kuten turvetuotannon valumavesille, minkä seurauksena valumavesien puhdistustuloksissa on suurta vaihtelua. Tässä väitöstyössä tutkittiin markkinoilla saatavilla olevien kemikaalien sopivuutta turvetuotannon humuspitoisille valumavesille. Tutkimuksessa testattiin epäorgaanisia (ferrisulfaatti, alumiinisulfaatti ja näiden sekoitus) ja orgaanisia (polyDADMAC, polyamiini, kitosaani ja tanniinipohjaisia polymeerejä) koagulanttikemikaaleja. Tutkimuksessa selvitettiin koagulanttien annostarpeet sekä erilaisten prosessiparametrien (vedenlaatu, sekoittaminen, pH ja lämpötila) vaikutus koagulanttien toimintaan. Laboratoriotutkimusten lisäksi väitöstyö sisälsi kenttämittauksia turvetuotannon valumavesien tyypillisten kemiallisen vesienkäsittelyn prosessiparametrien selvittämiseksi. Tutkituista koagulanteista rautasulfaatti oli tehokkain. Se tuotti hyvin laskeutuvaa flokkia ja poisti parhaiten valumavesien orgaanista ainesta. Rautasulfaatti vaati kuitenkin selkeästi suuremman annostuksen kuin esimerkiksi polyDADMAC ja kitosaani. Lisäksi puhdistettuun veteen jäi paljon rautaa ja vesi oli hapanta. Orgaanisilla kemikaaleilla saavutettiin myös kohtalainen/melko hyvä puhdistustulos, mutta lisää tutkimusta tarvitaan ennen kuin ne voivat olla vaihtoehtona epäorgaanisille kemikaaleille. Turvetuotannon valumaveden laatu vaihteli paljon. Valumaveden orgaanisen aineen määrän vaihtelulla oli suurin vaikutus kemikaalin annostukseen ja puhdistustulokseen. Sekoituksista kemiallisen käsittelyn flokkulaatiovaiheen sekoituksella oli suurempi vaikutus puhdistustulokseen kuin koagulaatiovaiheen sekoituksella. Tutkituilla turvetuotantoalueilla ei kuitenkaan ollut tällä hetkellä riittävää sekoitusta flokkulaatiovaiheessa. Tässä väitöstyössä esitetään parannuksia kemiallisen käsittelyn optimointiin paremman ja vakaamman puhdistustuloksen aikaansaamiseksi humuspitoisille vesille

Function and biomass production of willow wetlands applied in the polishing phase of sewage treatment in cold climate conditions

Abstract Willow wetlands can offer a low-cost solution for recovery of nutrients contained in sewage water and simultaneously produce plant biomass, which can be used in energy production. Willow (Salix spp.) is considered an excellent crop for this purpose, due to its good nutrient uptake and biomass production. Although willow wetlands have been used in sewage treatment in e.g. Denmark, Sweden and southern Finland, their use in northern regions is challenging due to the detrimental effects cold climate conditions can have on plant survival rates and wastewater purification efficiency. In this study, a pilot constructed wetland in northern Finland receiving effluent from a small-scale wastewater treatment plant was investigated. Four willow varieties were planted (Gudrun, Karin, Klara and one local variety) and retention of nutrients in the wetland and willow plant survival rate, biomass production and nutrient uptake were evaluated. Good retention of nutrients (e.g. Tot. N 66–86% and Tot. P 30–87%) was achieved throughout the study period. After two growing seasons, the variety Gudrun showed the best survival rate and significantly higher biomass production (5.7 t/ha) than Karin, Klara and the local variety (1.7, 3.0 and 0.02 t/ha, respectively). Thus, willow wetlands are suitable systems for nutrient recovery from pre-treated wastewater in cold climate regions. However, the willow variety used should be chosen carefully, as there can be significant differences in survival rate and biomass production between varieties

Evaluating the influence of pH adjustment on chemical purification efficiency and the suitability of industrial by-products as alkaline agents

Abstract Metal salts of iron are currently used in several treatment facilities purifying peat extraction runoff water. Although chemical purification is considered best available technology for the treatment of this natural humic water, fluctuations in purification efficiency occur with low pH (3–4) and high metal concentration found in treated waters. The need for pH neutralisation increases the costs and overall environmental impacts related to chemical purification. The use of industrial by-products can decrease costs while supporting the sustainable use of natural resources and the principle of a circular economy. This study investigated the suitability of a range of calcium-based alkaline products (including by-products of the paper, cement and mineral industries) for neutralisation of chemically treated runoff water. The influence of the time of pH adjustment relative to time of coagulant addition (before coagulant, after but within coagulation, during flocculation and after sedimentation) on purification efficiency was evaluated. The hypotheses that the physical form of the coagulant was a relevant factor affecting purification was also assessed. The best performing pH-adjusting products were cement kiln dust (CaO and SiO₂) and Mahtikalkki (Ca(OH)₂, CaCO₃ and CaO), by-products of the cement and paper industry, respectively. Time of pH adjustment in relation to time of coagulation addition had a significant influence on purification efficiency, especially when solid coagulant was used. Adjustment of pH at 30 s before coagulant dosing resulted in a negative effect on treatment results. Based on results obtained, suitable points of pH adjustment are during the flocculation stage or at the outlet of sedimentation, particularly if solid coagulants are used

Coagulation of humic waters for diffused pollution control and the influence of coagulant type on DOC fractions removed

Abstract This study examined the suitability of organic coagulants for treatment of typically humic peat extraction runoff water by comparing their performance with that of ferric sulphate (FS). The influence of coagulant type on dissolved organic carbon (DOC) fractions removed was analysed in detail using LC-OCD-OND (size exclusion liquid chromatography coupled with organic carbon and organic nitrogen detection) fractionation techniques. In general, lower coagulant dosage was needed under acidic (pH 4.5) than neutral (pH 6.5) conditions. Chitosan (Chit) and poly (diallyldimethyl) ammonium chloride (pDMAC) required significantly lower dosage (40–55%) than FS for acceptable purification, while a tannin-based coagulant (Tan2) required substantially higher dosage (55–75%) independent of water pH. FS demonstrated the best removal of DOC (<81%) and phosphorus (<93%) followed by pDMAC, while Chit and Tan2 achieved the highest removal of suspended solids (SS) (<58%), with flocs formed by Tan2 presenting the best settling properties. Higher molecular weight (MW) DOC fractions were more efficiently removed by all coagulants, with FS being the most efficient (biopolymers 69% and humic substances 91%), followed by Tan2. FS also displayed satisfactory removal of lower MW fractions (building blocks ∼46% and low MW neutrals 62%). Overall, FS was the best performing coagulant. Nevertheless, the organic polymers demonstrated satisfactory overall performance, achieving purification rates mostly inside the requirements set by Finnish environmental authorities

Removal of metals from mine drainage waters by in situ mineral sorbent-based pilot filter systems

Abstract Discharge of metal-containing wastewater streams into the environment is an environmental concern because these pollutants do not degrade and tend to bioaccumulate. A number of laboratory-based investigations on the effectiveness of a wide range of filter materials for metal removal from diluted wastewater streams have been reported. However, only a few pilot or full-scale investigations have been conducted. Therefore, this study investigated the metal retention capabilities of mineral-based filter materials (commercially available mineral product (5–15 mm), recycled mineral material (2–4 mm) and slag by-product (2–4 and 4–16 mm)) when used in pilot-scale filter systems under continuous operation in a closed mining area in North Ostrobothnia, Finland, between June and October 2017. The influence of material particle size on system function and on metal retention efficiency was also evaluated. The results revealed that system performance was dependent on material composition and particle size (smaller particle size being more effective). The highest metal removal efficiencies (Zn, Ni, Cd, Cu and Pb) and largest amount of water treated (per volume of material applied) were achieved by an aluminium oxide-based recycled mineral material (2–4 mm). While smaller-grained materials performed better in terms of removal efficiency, the removal rates achieved by coarser-grained, commercially available mineral product (5–15 mm) were comparable to those achieved by small-grained slag (2–4 mm). Full-scale systems using the recycled mineral product (2–4 mm) would have an approximately two-fold longer material replacement time than systems using the slag (2–4 mm). Replacement time for the larger-grained materials tested could not be determined, due to problems with freezing. Overall, the recycled mineral material tested can be recommended for full-scale tests, especially when high zinc removal rates are required

Removal of metals from wastewaters by mineral and biomass-based sorbents applied in continuous-flow continuous stirred tank reactors followed by sedimentation

Abstract Numerous studies have examined the performance of mineral and biomass-based sorbents for metal removal under laboratory conditions, but few pilot-scale tests have been performed on possible water purification systems in which these sorbents can be used. This study addressed this issue by evaluating the suitability of selected sorbents for use in continuous-flow continuous stirred tank reactors (CSTR) followed by sedimentation in laboratory and in situ pilot-scale experiments. Acid (HCl)-modified peat (M-Peat), a commercially available mineral sorbent containing mainly magnesium (Mg) carbonates, Mg oxides and Mg silicates (Mineral-P) and a calcium-rich ground granular blast furnace slag (by-product of stainless steel production (Slag) were tested for treatment of metallurgical industry wastewater (laboratory, pilot). Overall, higher metal removal was achieved from samples with higher initial metal concentrations. M-Peat achieved good removal of Zn (50–70%) and Ni (30–50%) in laboratory and pilot experiments. However, the poor settling characteristics of M-Peat can restrict its application in systems where sedimentation is the solid-liquid separation process applied. Mineral-P showed good performance in removing 65–85% of Zn present in the water and it performed similarly in laboratory and pilot tests. However, low concentrations of As and Ni leached from Mineral-P in all tests. Slag achieved good performance in treatment of the industrial wastewater, removing 65–80% of Zn and 60–80% of Pb during pilot tests. However, low concentrations of Cr and Cu were leached from Slag in a few tests. As a by-product of the same (metallurgical) industry, ground granular blast furnace slag is an excellent candidate for reducing Zn concentrations from industrial wastewater flows

Organic polyelectrolytes as the sole precipitation agent in municipal wastewater treatment

Abstract In municipal wastewater treatment, inorganic coagulants (IC), e.g. polyaluminium chloride (PAC), are normally used to remove pollutants such as dissolved and particulate nutrients, in a process called coagulation/flocculation. However, IC use has been linked to issues e.g. in effluent water post-treatment, sludge management and disposal (IC increase sludge volume and metal concentrations in sludge), etc., raising uncertainties about their overall cost-efficiency and environmental benefits. In this study, the suitability of organic coagulants (OC) as sole precipitation agents to replace IC (PAC) was investigated. A total of 10 synthetic (i.e. polyDADMACs and polyamines) and semi-natural (chitosan, starch, and tannin-based) OC products were tested in treatment of samples from primary sedimentation and secondary sedimentation stages of municipal wastewater treatment, and their performance was compared with that of PAC. The study was conducted using the jar test methodology. The coagulants were tested for their ability to remove target pollutants (e.g. BOD₇, COD, SS, tot-P, PO₄-P, tot-N) and form rapidly settling flocs. In general, higher (up to 60%) coagulant doses were needed in treatment of secondary wastewater samples than primary samples. In comparison with the OC doses required for effective treatment, the PAC doses were higher (up to 80%). In treatment of secondary wastewater samples, OC with high molecular weight (MW) and high charge density (CD) (e.g. pAmine1) achieved best removal of target pollutants (e.g. 72% SS, 87% PO₄-P, 88% BOD₇), followed by PAC. In treatment of primary wastewater, PAC performed best (removing e.g. 96% SS, 96% PO₄-P), closely followed by chitosan and polyamine products. Based on these results, polyamine products with high MW and (very) high CDs have the potential to act as the sole precipitation agent in both primary and secondary stages of municipal wastewater treatment. Further research is needed to determine the effect of residual coagulant on downstream water and sludge treatment processes (e.g. activated sludge process, sludge dewatering, etc.)

Removal of metals from mining wastewaters by utilization of natural and modified peat as sorbent materials

Abstract This study investigated metal removal efficiency of natural (N peat) and HCl treated peat (HCl peat) using batch sorption tests with real mining wastewaters. FTIR and XPS studies revealed that peat modification did not alter the structure of the sorbent. HCl peat exhihited higher maximum metal uptake capacity (22.4 mg Ni/g) than N peat (17.9 mg Ni/g). Sorbents removed arsenic most efficiently (80%, dosage 1 g/L). Optimum contact times ranged between 30–60 min. Our study revealed that although HCl peat had better settling properties, N peat displayed overall better purification performance, representing thus the most cost-effective and sustainable option

Treatment efficiency of package plants for on-site wastewater treatment in cold climates

Abstract Package plants (PP) are implemented around the world to provide on-site sanitation in areas not connected to a sewage network. The efficiency of PP has not been comprehensively studied at full scale, and the limited number of available studies have shown that their performance varies greatly. Their performance under cold climate conditions and the occurrence of micropollutants in PP effluents have not been sufficiently explored. PP are exposed to environmental factors such as low temperature, especially in cold regions with low winter temperatures and deep frost penetration, that can adversely influence the biochemical processes. The aim of this study was to investigate the treatment efficiency and possible effects of cold temperatures on PP performance, with focus on traditional contaminants (organics, solids, nutrients and indicator bacteria) and an additional assessment of micropollutants on two PP. Eleven PP hosting different treatment processes were monitored. Removal of biological oxygen demand (BOD) was high in all plants (>91%). Six out of the 11 PP provided good phosphorus removal (>71%). Small degrees of nitrification were observed in almost all the facilities, despite the low temperatures, while denitrification was only observed in two plants which achieved the highest nitrification rates (>51%) and had sludge recirculation. No strong correlation between wastewater temperature and BOD, nutrients and indicator bacteria concentration in the effluents was found. The high data variability and the effects of other process parameters as well as snow-melt water infiltration are suggested as possible reasons for the lack of correlation. However, weak negative relations between effluent concentrations and wastewater temperatures were detected in specific plants, indicating that temperature does have effects. When managed adequately, package plants can provide high BOD and phosphorus removal, but nitrogen and bacteria removal remain challenging, especially at low temperatures. Pharmaceutical compounds were detected in the effluents at concentrations within or above ranges reported for large treatment plants while phthalate ester concentrations were below commonly reported effluent concentrations

Solids management in freshwater-recirculating aquaculture systems:effectivity of inorganic and organic coagulants and the impact of operating parameters

Abstract Coagulants are widely used for solids (uneaten food, faeces, etc.) management in recirculating aquaculture systems (RAS), but no recent research has been performed on the effectiveness of different coagulants in treatment of aquaculture sludge. This study examined the effectivity of selected inorganic (polyaluminium chloride, PAC) and organic products (polyamine- and starch-based) as coagulant agents for solids management in RAS. Reductions in residual concentrations of total phosphorus (tot-P), phosphate‑phosphorus (PO₄-P), suspended solids (SS) total nitrogen (tot-N), nitrate‑nitrogen (NO₃-N), ammonium‑nitrogen (NH₄-N), aluminium (Al) and chemical oxygen demand (COD) in reject water were determined. The effect of process parameters (coagulant type, dose, mixing and sedimentation time) on sludge treatment was also evaluated. The PAC products tested were most effective at concentrating pollutants (Tot-P, PO₄-P, SS, COD) in RAS sludge into the solid phase. The organic products tested, especially a high-molecular-weight polyamine product (pAmine1), achieved good performance and can be considered a valid alternative to inorganic salts. At optimum dose, PAC (dose ₃2 mg/L) and pAmine1 (dose 15 mg/L) removed, respectively, 99.₄% and 82.8% of turbidity, 98.2% and 65.₄% of PO₄-P and 97.7% and 7₃.6% of SS. The mixing time applied in flocculation and the time allowed for sedimentation had significant effects on coagulant performance, with the organic coagulants being most affected. Flocculation times of 5–15 min and sedimentation times of 15–60 min showed good results and can be used as a starting point in process optimisation with both inorganic and organic coagulants. The use of coagulants for treatment of RAS sludge enhances flock formation and improves particle settling characteristics, substantially decreasing nutrient, organics and solids concentration in reject water