A detection system for simultaneously determining the concentration of ammonium, nitrate/nitrite in a wastewater sample comprising: a sample loop having an internal flow path in fluid communication with a wastewater sample comprising water, ammonium, nitrate/nitrite, and particulate matter, the sample loop comprising a loop outlet in fluid communication with a feed conduit, a first one-way valve assembly configured to be open to the feed conduit, and a first pump assembly in fluid communication with the feed conduit; a first alkaline stream in fluid communication with the feed conduit to mix the first alkaline solution with the wastewater sample and convert the ammonium to ammonia and generate a first stream; a first filter assembly in fluid communication with the first stream to remove at least a portion of the particulate matter from the sample stream and generate a filtered first stream; a first gas-diffusion cell comprising a first acid solution feed for (i) removing the ammonia from the filtered first stream to generate second stream comprising the nitrate/nitrite and for (ii) converting the removed ammonia back to ammonium to generate a third stream comprising the ammonium; a first conductivity detector assembly for determining the concentration of ammonium in the third stream; a plurality of reducing columns, each reducing column individually comprising a reducing metal to convert the nitrate/nitrite in the second stream to ammonia and to generate a fourth stream comprising the ammonia produced by reducing the nitrate/nitrite, the plurality of reducing columns configured for parallel flow, and a valve assembly for each of the reducing columns configured open the flow of the second stream to the respective reducing columns one at a time; a second gas-diffusion cell comprising a second acid solution feed for (i) removing the ammonia produced by reducing the nitrate/nitrite in the fourth stream and (ii) converting the removed ammonia produced by reducing the nitrate/nitrite back to ammonium to generate a fifth stream comprising the ammonium; a second conductivity detector assembly for determining the concentration of ammonium in the fifth stream from which the concentration of the nitrate/nitrite is determined. a sample loop having an internal flow path in fluid communication with a wastewater sample comprising water, ammonium, nitrate/nitrite, and particulate matter, the sample loop comprising a loop outlet in fluid communication with a feed conduit, a first one-way valve assembly configured to be open to the feed conduit, and a first pump assembly in fluid communication with the feed conduit; a first alkaline stream in fluid communication with the feed conduit to mix the first alkaline solution with the wastewater sample and convert the ammonium to ammonia and generate a first stream; a first filter assembly in fluid communication with the first stream to remove at least a portion of the particulate matter from the sample stream and generate a filtered first stream; a first gas-diffusion cell comprising a first acid solution feed for (i) removing the ammonia from the filtered first stream to generate second stream comprising the nitrate/nitrite and for (ii) converting the removed ammonia back to ammonium to generate a third stream comprising the ammonium; a first conductivity detector assembly for determining the concentration of ammonium in the third stream; a plurality of reducing columns, each reducing column individually comprising a reducing metal to convert the nitrate/nitrite in the second stream to ammonia and to generate a fourth stream comprising the ammonia produced by reducing the nitrate/nitrite, the plurality of reducing columns configured for parallel flow, and a valve assembly for each of the reducing columns configured open the flow of the second stream to the respective reducing columns one at a time; a second gas-diffusion cell comprising a second acid solution feed for (i) removing the ammonia produced by reducing the nitrate/nitrite in the fourth stream and (ii) converting the removed ammonia produced by reducing the nitrate/nitrite back to ammonium to generate a fifth stream comprising the ammonium; a second conductivity detector assembly for determining the concentration of ammonium in the fifth stream from which the concentration of the nitrate/nitrite is determined.