<\/span><\/h2>\nTraditional ammonia measurement relies on colorimetric methods (such as the salicylate or Nessler reactions) that require reagent addition, sample conditioning, and laboratory analysis. These methods produce accurate results but are unsuitable for continuous monitoring: they generate hazardous waste, consume reagents on every measurement cycle, and need operator intervention every 4-8 hours.<\/p>\n
Ion-selective electrode (ISE) technology takes a fundamentally different approach. An ammonia-sensitive membrane\u2014typically a gas-permeable hydrophobic polymer\u2014separates the sample water from an internal electrolyte solution. Ammonia molecules diffuse through the membrane and alter the pH of the internal electrolyte, which an internal pH electrode measures. The resulting potential is proportional to the ammonia concentration in the sample.<\/p>\n
Shanghai ChiMay’s Ammonia Nitrogen Sensor<\/strong> uses this ISE principle with a measurement range of 0-1000 mg\/L NH\u2083-N<\/strong> and accuracy of \u00b10.1 mg\/L<\/strong> in the 0-50 mg\/L range most relevant to agricultural reuse monitoring. The sensor operates without reagents, produces no chemical waste, and provides a continuous output via Modbus RTU\/TCP<\/strong> communication.<\/p>\nKey technical characteristics for reuse monitoring:<\/p>\n
\n- Response time:<\/strong> T90 response within 120 seconds<\/strong>, enabling detection of ammonia breakthrough events in near-real time.<\/li>\n
- Temperature compensation:<\/strong> Automatic compensation from 0-50\u00b0C<\/strong> using an integrated temperature sensor.<\/li>\n
- pH dependency:<\/strong> Ammonia ISE measurement is pH-dependent because the ammonia-ammonium equilibrium shifts with pH. The sensor must be paired with a pH measurement for accurate speciation, which Shanghai ChiMay addresses through its multi-parameter sensor or a standalone pH electrode.<\/li>\n
- Interference management:<\/strong> Potassium ions (K\u207a) can interfere with ammonia ISE measurement at high concentrations. Shanghai ChiMay’s membrane formulation achieves a K\u207a\/NH\u2084\u207a selectivity ratio better than 100:1<\/strong>, ensuring reliable ammonia measurement even in waters with elevated potassium from agricultural fertilizer runoff.<\/li>\n<\/ul>\n
<\/span>UV Absorption Technology for Continuous COD Monitoring<\/span><\/h2>\nCOD measurement by the standard laboratory method (dichromate oxidation at 150\u00b0C for two hours) is time-consuming, generates hazardous chromium waste, and cannot provide real-time data. UV absorption spectroscopy offers a reagent-free alternative that correlates absorbance at 254 nm<\/strong> with the concentration of aromatic and conjugated organic compounds in the water.<\/p>\nUV absorption does not measure the exact same chemical parameter as dichromate COD, but the correlation between UV254 absorbance and COD is strong enough for continuous monitoring in most wastewater and reuse applications, with typical correlation coefficients (R\u00b2) of 0.92-0.98<\/strong>.<\/p>\nShanghai ChiMay’s COD Sensor<\/strong> uses a dual-beam UV absorption design with a measurement range of 0-500 mg\/L COD<\/strong> and accuracy of \u00b12 mg\/L<\/strong>. The dual-beam configuration compensates for lamp aging and window fouling by continuously referencing a clean beam path against the measurement beam, maintaining accuracy over extended deployment periods.<\/p>\nKey technical characteristics for agricultural reuse monitoring:<\/p>\n
\n- No reagent consumption:<\/strong> Unlike laboratory COD methods, the UV sensor requires zero chemicals, eliminating supply-chain risk and hazardous waste disposal.<\/li>\n
- Response time:<\/strong> Near-instantaneous measurement with a T90 response under 30 seconds<\/strong>, enabling detection of organic load spikes that would be invisible to periodic grab sampling.<\/li>\n
- Fouling management:<\/strong> An integrated compressed air cleaning system or optional wiper mechanism keeps the optical window clear in waters with moderate suspended solids loading.<\/li>\n
- Site-specific correlation:<\/strong> A one-time side-by-side comparison of UV sensor readings with laboratory COD results establishes a site-specific correlation factor that converts the UV output to COD-equivalent values.<\/li>\n<\/ul>\n
<\/span>Sensor Placement Strategy for Agricultural Reuse Monitoring<\/span><\/h2>\nA typical agricultural reuse treatment train with continuous ammonia and COD monitoring includes these measurement points:<\/p>\n
\n- After secondary biological treatment (nitrification):<\/strong> The ammonia sensor verifies complete nitrification before the water enters the polishing stage. A rising ammonia reading signals nitrification failure and triggers process investigation before non-compliant water reaches the reuse distribution.<\/li>\n
- After filtration (sand or membrane):<\/strong> The COD sensor confirms that organic matter has been reduced below the Class A threshold. If COD exceeds the alarm setpoint, the water is automatically diverted away from the reuse storage tank.<\/li>\n
- In the reuse distribution network:<\/strong> Both ammonia and COD sensors at the distribution network outlet provide continuous verification that the water reaching the agricultural end user meets Class A limits.<\/li>\n
- Return flow from agricultural drainage:<\/strong> Monitoring ammonia and COD in drainage water returning from irrigated fields helps operators assess whether the applied reuse water is contributing to nutrient loading in receiving waters.<\/li>\n<\/ul>\n
<\/span>Comparing Continuous Sensors to Grab Sampling<\/span><\/h2>\nThe transition from grab sampling to continuous monitoring for ammonia and COD in agricultural reuse delivers measurable improvements:<\/p>\n
\n- Detection speed:<\/strong> Continuous sensors detect parameter excursions within 2-5 minutes<\/strong>, compared with 4-24 hours<\/strong> for grab sampling with laboratory turnaround.<\/li>\n
- Data density:<\/strong> Continuous monitoring produces 288 data points per day<\/strong> (at 5-minute intervals), compared with 1-4 data points per day<\/strong> from grab sampling. That density enables trend analysis, early warning, and automated compliance reporting.<\/li>\n
- Operating cost:<\/strong> After the initial capital investment, continuous sensors cost approximately USD 3,000-5,000 per year<\/strong> in maintenance and consumables per parameter, compared with USD 15,000-30,000 per year<\/strong> in laboratory fees for grab sampling at four-times-daily frequency.<\/li>\n
- Audit defensibility:<\/strong> Continuous data with tamper-evident timestamps provides stronger compliance evidence during regulatory audits than grab samples, which are subject to chain-of-custody challenges.<\/li>\n<\/ul>\n
Shanghai ChiMay supports agricultural reuse operators with application engineering to design the optimal sensor placement strategy, establish site-specific correlations, and integrate continuous data into SCADA systems for automated compliance reporting.<\/p>\n","protected":false},"excerpt":{"rendered":"
title: “Continuous Ammonia and COD Verification for Agricultural Reuse Under EU Class A: A Shanghai ChiMay Technical Guide” date: 2026-07-20 perspective: Technical Deep-Dive theme: Water Recycling & Circular Water Economy Continuous Ammonia and COD Verification for Agricultural Reuse Under EU Class A: A Shanghai ChiMay Technical Guide The Short Version The EU 2025 Water Reuse…<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_kad_post_transparent":"","_kad_post_title":"","_kad_post_layout":"","_kad_post_sidebar_id":"","_kad_post_content_style":"","_kad_post_vertical_padding":"","_kad_post_feature":"","_kad_post_feature_position":"","_kad_post_header":false,"_kad_post_footer":false},"categories":[1],"tags":[],"translation":{"provider":"WPGlobus","version":"2.12.0","language":"es","enabled_languages":["en","es","fr","ru","ar"],"languages":{"en":{"title":true,"content":true,"excerpt":false},"es":{"title":false,"content":false,"excerpt":false},"fr":{"title":false,"content":false,"excerpt":false},"ru":{"title":false,"content":false,"excerpt":false},"ar":{"title":false,"content":false,"excerpt":false}}},"_links":{"self":[{"href":"https:\/\/shchimay.com\/es\/wp-json\/wp\/v2\/posts\/31320"}],"collection":[{"href":"https:\/\/shchimay.com\/es\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/shchimay.com\/es\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/shchimay.com\/es\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/shchimay.com\/es\/wp-json\/wp\/v2\/comments?post=31320"}],"version-history":[{"count":0,"href":"https:\/\/shchimay.com\/es\/wp-json\/wp\/v2\/posts\/31320\/revisions"}],"wp:attachment":[{"href":"https:\/\/shchimay.com\/es\/wp-json\/wp\/v2\/media?parent=31320"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/shchimay.com\/es\/wp-json\/wp\/v2\/categories?post=31320"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/shchimay.com\/es\/wp-json\/wp\/v2\/tags?post=31320"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}